Glossary of cellular and molecular biology (0–L)
This glossary of cellular and molecular biology is a list of definitions of terms and concepts commonly used in the study of cell biology, molecular biology, and related disciplines, including genetics, biochemistry, and microbiology. It is split across two articles:
This glossary is intended as introductory material for novices. It has been designed as a companion to Glossary of [genetics and evolutionary biology], which contains many overlapping and related terms; other related glossaries include Glossary of virology and Glossary of chemistry.
0–9
One of two ends of a single linear strand of or, specifically the end at which the chain of terminates at the third carbon atom in the furanose ring of or . By convention, sequences and structures positioned nearer to the 3'-end relative to others are referred to as. Contrast '.
Image:Nukleotid num.svg|300px|thumb|right|A ring with the carbon atoms numbered 1' through 5' according to chemical convention. The ' is said to be upstream; the ' is said to be downstream. Bonds to a generic and a phosphate group are also shown.
A specially altered attached to the of some as part of the set of which convert raw transcripts into mature RNA products. The precise structure of the 5' cap varies widely by organism; in eukaryotes, the most basic cap consists of a bonded to the triphosphate group that terminates the 5'-end of an RNA sequence. Among other functions, capping helps to regulate the export of mature RNAs from the, prevent their degradation by, and promote in the cytoplasm. Mature can also be decapped.
See '.
One of two ends of a single linear strand of or, specifically the end at which the chain of terminates at the fifth carbon atom in the furanose ring of or . By convention, sequences and structures positioned nearer to the 5'-end relative to others are referred to as. Contrast '.
See '.
A
Having no.
A biochemical compound consisting of a molecule to which an acetyl group is attached via a high-energy thioester bond. of coenzyme A occurs as part of the of, , and , after which it participates as an energy carrier in several important, notably the, in which hydrolysis of the acetyl group releases energy which is ultimately captured in 11 and one.
The covalent attachment of an acetyl group to a chemical compound, protein, or other biomolecule via an esterification reaction with acetic acid, either spontaneously or by catalysis. Acetylation plays important roles in several and in. Contrast '.
Any of a class of which catalyze the covalent bonding of an acetyl group to another compound, protein, or biomolecule, a process known as.
Having a positioned very close to one end of the chromosome, as opposed to or.
The local change in voltage that occurs when the of a specific location along the of a rapidly depolarizes, such as when a nerve impulse is transmitted between.
See '.
A type of that increases the of a or set of genes. Most activators work by binding to a specific located within or near an or and facilitating the binding of and other transcription machinery in the same region. See also '; contrast '.
The region of an to which one or more bind, causing the substrate or another molecule to undergo a chemical reaction. This region usually consists of one or more residues which, when the enzyme is properly, are able to form temporary chemical bonds with the atoms of the substrate molecule; it may also include one or more additional residues which, by interacting with the substrate, are able to catalyze a specific reaction involving the substrate. Though the active site constitutes only a small fraction of all the residues comprising the enzyme, its specificity for particular substrates and reactions is responsible for the enzyme's biological function.
Transport of a substance across a against a concentration gradient. Unlike, active transport requires an expenditure of energy.
The covalent attachment of any acyl group to a chemical compound, protein, or other biomolecule via the substitution of the acyl group for a hydrogen atom, either spontaneously or by enzymatic catalysis. is a type of acylation.
A used as one of the four standard nucleobases in both and molecules. Adenine forms a with in DNA and with in RNA.
One of the four standard used in molecules, consisting of an with its N9 nitrogen to the C1 carbon of a sugar. Adenine bonded to is known as, which is the version used in.
A diphosphate consisting of attached to two consecutive groups via high-energy ester bonds. ADP can be to produce and thus is a precursor for its synthesis; it can also be dephosphorylated into.
A consisting of attached to a single group via a high-energy ester bond. Additional phosphate groups can be added to AMP to produce and ; the serves as a second messenger in some signaling pathways.
A consisting of attached to three consecutive groups via high-energy ester bonds. The conversion of ATP into or via hydrolysis of these phosphates releases energy which is used to drive the majority of energy-consuming chemical reactions in all living cells, and hence ATP functions as a universal and ubiquitous energy carrier which is often referred to as the "molecular currency" of intracellular. It is continuously regenerated via of ADP and AMP by enzymes such as ATP synthase. Like other nucleoside triphosphates, it also serves as a precursor for synthesis.
A type of cell found in, containing large -filled.
One of three main biologically active of the , along with and. The A-form helix has a right-handed twist with 11 per full turn, only slightly more compact than B-DNA, but its bases are sharply tilted with respect to the helical axis. It is often favored in dehydrated conditions and within sequences of consecutive nucleotides ; it is also the primary conformation adopted by and.
1. Describing conditions in which gaseous or dissolved diatomic oxygen is present. Aerobic environments are said to be oxygenated.
2. Describing an organism, pathway, or process that requires or makes use of diatomic oxygen; e.g.. Contrast '.
Any pair of organisms which are related genetically and both affected by the same. For example, two cousins who both have blue eyes are an affected relative pair since they are both affected by the that codes for blue eyes.
A laboratory method used in molecular biology to extract and isolate such as the DNA of from certain cell types, commonly bacterial cells.
One of multiple alternative versions of an individual, each of which is a viable sequence occupying a given position, or, on a. For example, in humans, one allele of the eye-color gene produces blue eyes and another allele of the same gene produces brown eyes.
Any that differs from an ordinary in size, form, or behavior and which is responsible for determining the sex of an organism. In humans, the and the are sex chromosomes.
A common structural in the secondary structures of consisting of a right-handed helix conformation resulting from hydrogen bonding between residues which are not immediately adjacent to each other.
A regulated phenomenon of eukaryotic in which specific or parts of exons from the same are variably included within or removed from the final, mature transcript. A class of, alternative splicing allows a single to code for multiple protein and greatly increases the diversity of proteins that can be produced by an individual. See also '.
One of three used in the ; in, it is specified by the nucleotide triplet. The other two stop codons are named and.
Any of a class of organic compounds whose basic structural formula includes a central carbon atom bonded to amine and carboxyl functional groups and to a variable side chain. Out of nearly 500 known amino acids, a set of 20 are coded for by the and incorporated into long polymeric chains as the building blocks of and hence of and. The specific sequences of amino acids in the polypeptide chains that form a protein are ultimately responsible for determining the protein's structure and function.
File:Amino acid generic structure.png|500px|thumb|right|Every has the same basic structural formula, consisting of a central carbon atom bonded to three major substituents: one amino group, one carboxyl group, and one variable side chain. The side chain, which can range from a simple methyl group to more complex functional groups such as a double-ringed indole, gives each particular amino acid its unique identity. During, amino acids are joined into a linear chain by condensation reactions which create between the carboxyl group of one amino acid and the amino group of an adjacent amino acid. The first and last amino acids in the chain are said to be and, respectively, in reference to the unbonded amino group of the first amino acid and the unbonded carboxyl group of the last.
See '.
Any of a set of enzymes which catalyze the transesterification reaction that results in the attachment of a specific to one of its cognate molecules, forming an. Each of the 20 different amino acids used in the is recognized and attached by its own specific synthetase enzyme, and most synthetases are cognate to several different tRNAs according to their specific.
A to which a cognate is chemically bonded; i.e. the product of a transesterification reaction catalyzed by an. Aminoacyl-tRNAs bind to the of the during.
Any DNA or RNA sequence or fragment that is the source and/or product of an reaction. The term is most frequently used to describe the numerous copied fragments that are the products of the or, though it may also refer to sequences that are amplified naturally within a genome, e.g. by.
The of a biomolecule, in particular the production of one or more copies of a, known as an, either naturally or artificially, and especially implying many repeated replication events resulting in thousands, millions, or billions of copies of the target sequence, which is then said to be amplified.
Any reaction or process in which energy is expended in order to build complex substances such as macromolecules from simpler compounds, including aspects of growth and biosynthesis. Anabolic processes and tend to involve reductive steps that create high-enthalpy, low-entropy compounds such as proteins and nucleic acid polymers. Contrast '.
1. Describing conditions in which diatomic oxygen is entirely absent, as opposed to conditions.
2. Describing an organism that is able to survive and grow in the absence of diatomic oxygen, or a pathway or process characterized by the absence of diatomic oxygen; e.g..
The stage of and that occurs after and before, when the replicated chromosomes are segregated and each of the are moved to opposite sides of the.
The failure of one or more pairs of or to properly migrate to opposite sides of the cell during of or due to a defective. Consequently, both daughter cells are : one is missing one or more chromosomes while the other has one or more extra copies of the same chromosomes.
Having an abnormal number of, i.e. more than one.
The condition of a cell or organism having an abnormal number of one or more particular .
The of two molecules containing sequences, creating a molecule with . The term is used in particular to describe steps in laboratory techniques such as, where double-stranded DNA molecules are repeatedly into single strands by heating and then exposed to cooler temperatures, causing the strands to reassociate with each other or with complementary. The exact is strongly influenced by the length and specific sequence of the individual strands.
A gene that confers resistance to one or more specific antibiotic compounds. In molecular cloning, are often designed to carry antibiotic resistance genes as alongside other genes of interest, because it permits the artificial selection of successfully cell populations when the cells are cultured in the presence of the antibiotic.
Any of a diverse family of known as capable of binding specifically but reversibly via non-covalent interactions to a particular or. Antibodies are generated as part of an organism's immune response to the introduction of a specific antigen into a host organism, and their binding of the antigen frequently counteracts or inhibits any biological activity the antigen may have. Antibodies have a characteristic Y-shaped structure consisting of a and held together by disulfide bonds.
A consecutive within a which the three nucleotides of a within an transcript. During, each tRNA recruited to the contains a single anticodon triplet that pairs with its complementary codon from the mRNA sequence, allowing each codon to specify a particular to be added to the growing peptide chain. Anticodons containing in the first position are capable of pairing with more than one codon due to a phenomenon known as.
Any agent that, upon introduction into an immunocompetent organism, stimulates a response from the organism's immune system that results in the production of one or more which can bind to it specifically; in this sense the term is synonymous with. Antigens may be pure substances, mixtures of substances, or particulate matter such as cells or cell fragments. Broader definitions may include substances that can bind to a specific antibody but are not themselves immunogenic, i.e. those which are only able to stimulate antibody production when combined with a.
Any molecule that functions as an antagonist to a process, limiting or inhibiting normal cellular metabolism; i.e. a metabolic poison.
Any compound that suppresses normal in a cell or population of cells.
A which helps to regulate cell growth and suppress tumors when functioning correctly, such that its absence or malfunction can result in uncontrolled cell growth and possibly cancer. Compare '.
The contrasting orientations of the two of a which are parallel to each other but with opposite. For example, the two strands of a molecule run side-by-side but in opposite directions with respect to chemical numbering conventions, with one strand oriented -to- and the other 3'-to-5'.
A which works by exchanging two different ions or small molecules across a in opposite directions, either at the same time or consecutively.
See '.
A molecule containing an sequence that is to a sense strand, such as a, with which it readily, thereby inhibiting the sense strand's further activity. Many different classes of naturally occurring RNA such as function by this principle, making them potent gene in various mechanisms. Synthetic antisense RNA has also found widespread use in gene studies, and in practical applications such as antisense therapy.
Lacking a, i.e. a discrete, membrane-bound organelle enclosing the cell's, used especially of cells which normally have a nucleus but from which the nucleus , and also of specialized cell types that develop without nuclei despite that the cells of other tissues comprising the same organism ordinarily do have nuclei.
The process by which contraction of the side of a cell causes the cell to assume a wedge-shaped morphology. The process is common during early development, where it is often coordinated across many adjacent cells of an layer simultaneously in order to generate bends or folds in developing.
A highly regulated form of that occurs in organisms.
Any artificial,, or molecule, or, which functions as a by binding selectively to one or more specific target molecules, usually other nucleic acids or, and often a family of such molecules. The term is used in particular to describe short nucleic acid fragments which have been randomly generated and then artificially selected ' by procedures such as SELEX. Aptamers are useful in the laboratory as, particularly in applications where conventional protein are not appropriate.
A set of laboratory methods used in the of a from free, i.e. without relying on an existing.
Any process by which chemical compounds containing biologically relevant elements are uptaken by microorganisms and incorporated into complex in order to synthesize various cellular components. In contrast, a uses the energy released by decomposing exogenous molecules to power the cell's and out of the cell, instead of reusing them to build new molecules.
In animal cells, a star-shaped system of non- that radiates from a or from either of the poles of the during the early stages of cell division.
The failure of to properly pair with each other during. Contrast ' and '.
A single containing two or more physically attached copies of the normal as a result of either a natural internal or any of a variety of methods. The resulting compound chromosome effectively carries two or more doses of all genes and sequences included on the X, yet functions in all other respects as a single chromosome, meaning that haploid 'XX' will be produced by and inherited by progeny. In mechanisms such as in which the sex of an organism is determined by the total dosage of X-linked genes, an abnormal 'XXY', fertilized by one XX gamete and one Y gamete, will develop into a female.
The or digestion of a by its own ; or of a particular enzyme by another instance of the same enzyme. See also '.
The orderly degradation and recycling of dysfunctional or unnecessary cellular components by the cell's own enzymes as part of a carefully regulated, -dependent pathway. Autophagic programs play important roles in nutrient-deprived and but also help maintain in healthy cells.
Any that is not an and hence is not involved in the determination of the sex of an organism. Unlike the sex chromosomes, the autosomes in a cell exist in pairs, with the members of each pair having the same structure, morphology, and genetic.
A cell or organism that is for a at which the two homologous are identical by descent, both having been derived from a single gene in a common ancestor. Contrast .
The growth of a multicellular organism due to an increase in the size of its cells rather than an increase in the number of cells.
Describing a in which only a single species, variety, or strain is present, and which is therefore entirely free of contaminating organisms including symbiotes and parasites.
Any supernumerary molecule which is not a duplicate of nor to any of the standard complement of normal "A" chromosomes comprising a genome. Typically very small and devoid of structural genes, B chromosomes are by definition not necessary for life. Though they occur naturally in many eukaryotic species, they are and thus even between closely related individuals.
A that reverses the effect of a previous which had inactivated a gene, thus restoring function. See also '.
An abbreviation of and.
A pair of two on or strands which are loosely attracted to each other via hydrogen bonding, a type of non-covalent electrostatic interaction between individual atoms in the purine or pyrimidine rings of the complementing bases. This phenomenon, known as base pairing, is the mechanism underlying the that commonly occurs between nucleic acid polymers, allowing two molecules to combine into a more energetically stable molecule, as well as enabling certain individual strands to. The ability of consecutive base pairs to stack one upon another contributes to the long-chain structures observed in both and molecules.
A measure of the level of a or genes prior to a perturbation in an experiment, as in a negative control. Baseline expression may also refer to the expected or historical measure of expression for a gene.
A computer algorithm widely used in for and comparing primary biological sequence information such as the of DNA or RNA or the of proteins. BLAST programs enable scientists to quickly check for homology between two or more sequences by directly comparing the nucleotides or amino acids present at each position within each sequence; a common use is to search for matches between a specific query sequence and a digital sequence database such as a, with the program returning a list of sequences from the database which resemble the query sequence above a specified threshold of similarity. Such comparisons can permit the identification of an organism from an unknown sample or the inference of evolutionary relationships between genes, proteins, or species.
The "standard" or classical of the ', thought to represent an average of the various distinct conformations assumed by very long DNA molecules under physiological conditions. The B-form double helix has a right-handed twist with a diameter of 23.7 ångströms and a of 35.7 ångströms or about 10.5 per full turn, such that each nucleotide pair is rotated 36° around the helical axis with respect to its neighboring pairs. See also ' and '.
The by which molecules are into simpler molecules, generating in the process. This occurs via a series of enzyme-catalyzed reactions which oxidize the beta carbon of the fatty acid chain and ultimately convert it into a carbonyl group, which is then susceptible to nucleophilic attack by another molecule of, causing thiolysis of the bond between the alpha and beta carbons; this process can be repeated to sequentially digest long chains of hydrocarbons into shorter chains, generating an additional molecule of acetyl-CoA with every cycle. In prokaryotes, beta oxidation occurs in the cytosol, while in eukaryotes it primarily takes place in the inner membrane or in.
A common mechanism of in which two move in opposite directions away from the same ; this results in a where the molecule is locally separated into two.
The separation of a single entity into exactly two discrete entities closely resembling the original. The term refers in particular to a type of used by such as bacteria, whereby a single divides evenly into two which are genetically identical to each other and to the parent. Binary fission is preceded by of the parent cell's DNA, rapid growth of the, and various other processes which ensure even distribution of the cell's contents between the two progeny, but is generally a quicker and simpler process than the and that occur in.
A region of a macromolecule such as a nucleic acid or a protein that directly participates in chemical interactions with another molecule. A wide variety of chemical interactions of varying strength and specificity can be described as "binding"; they may be long-term or transient, reversible or irreversible, and may rely upon relatively weak intermolecular forces or much stronger covalent bonds. Binding sites are defined by the spatial proximity of one or more having functional groups with particular chemical properties. For example, the of polypeptides in such a way that particular amino acids are positioned near each other in the protein's may confer chemical properties that permit the interaction of those residues with a particular. Similarly, a specific sequence of nucleobases in a DNA molecule may function as a for a. Whether and how the binding site functions depends on the precise spatial arrangement of the interacting residues and their physical accessibility to potential binding partners; thus mutations or changes in the chemical environment such as can dramatically alter functionality. See also '.
Any analytical method that measures or qualifies the presence, effect, or potency of a substance within or upon a biological system, either directly or indirectly, e.g. by quantifying the concentration of a particular chemical compound within a sample obtained from living organisms, cells, or tissues, and ideally under controlled conditions that compare a sample subjected to an experimental treatment with an unmanipulated sample, so as to permit inferences about the effect of the treatment upon some measured variable.
A subdiscipline of both biology and chemistry which studies the chemical basis of biological phenomena, focusing on understanding the chemical reactions and interactions that occur between and give rise to the processes that define and characterize living systems. It is closely related to and largely overlaps with.
The branch of and that studies the flow of energy through living systems, in particular how organisms acquire, produce, transform, and utilize energy in order to perform biochemical work such as.
A community of symbiotic microorganisms, especially bacteria, where cells produce and embed themselves within a slimy, sticky composed of various high-molecular weight biopolymers, to each other and sometimes also to a, which may be a biotic or abiotic surface. Many bacteria can exist either as independent single cells or switch to a physiologically distinct biofilm phenotype; those that create biofilms often do so in order to shelter themselves from harmful environments. Cells residing within biofilms can easily share nutrients and, and subpopulations of cells may to perform specialized functions supporting the whole biofilm.
A measurable indicator of some biological state, especially a compound or whose presence or absence in a biological system is a reliable sign of a normal or abnormal process, condition, or disease. Things that may serve as biomarkers include direct measurements of the concentration of a particular compound or molecule in a tissue or fluid sample, or any other characteristic physiological, histological, or radiographic signal. They are regularly used as predictive or diagnostic tools in clinical medicine and laboratory research.
Any metallic element found naturally in small but measurable amounts in biological contexts. Metal ions play important roles in many biochemical processes and some are essential for normal function in living organisms, especially iron, zinc, copper, manganese, magnesium, potassium, sodium, and calcium.
Any difference in the concentration of between two spaces within a biological system, whether,, across a, or between different cells or different parts of a tissue or organ system. Gradients of one kind or another drive virtually all biochemical processes occurring within and between cells, as natural systems tend to move toward a thermodynamic equilibrium where concentrations are uniformly distributed in all spaces and no gradients exist. Gradients thus cause chemical reactions to occur in particular directions, which can be used by cells to accomplish essential biological functions, including,, and movement of ions and solutes into and out of cells and organelles. It is often necessary for cells to continuously regenerate gradients such as in order to permit these processes to continue.
Any molecule or chemical compound involved in or essential to one or more biological processes within a biological system, especially large such as,,, and, but also broadly inclusive of smaller molecules such as,, and which are consumed or produced by biochemical reactions, often as part of. Most biomolecules are organic compounds; some are produced naturally within or , while others can only be obtained from the organism's environment.
See '.
Any of a variety of molecular biology methods by which or chromatographically separated,, or samples are transferred from a support medium such as a polyacrylamide or agarose gel onto an immobilizing carrier such as a nitrocellulose or PVDF membrane. Some methods involve the transfer of molecules by capillary action, while others rely on the transport of charged molecules by electrophoresis. The transferred molecules are then visualized by colorant staining, by autoradiography, or by for specific sequences or with or to chemiluminescent reporters.
A term used to describe the end of a molecule where the terminal nucleobases on each are with each other, such that neither strand has a single-stranded "overhang" of unpaired bases. This is in contrast to a so-called "", where an overhang is created by one strand being one or more bases longer than the other. Blunt ends and sticky ends are relevant when multiple DNA molecules, e.g. in, because sticky-ended molecules will not readily to each other unless they have matching overhangs; blunt-ended molecules do not anneal in this way, so special procedures must be used to ensure that fragments with blunt ends are joined in the correct places.
A synthetic with a chemical structure similar to, the only difference being the substitution of a bromine atom for the methyl group of the.
C
A that restricts the of other genes to specific tissues or body parts in an organism, typically by producing which variably inhibit or permit of the other genes in different. The term is used most commonly in plant genetics.
Any of a class of which are dependent on calcium ions and whose extracellular function as mediators of cell–cell adhesion at in eukaryotic tissues.
An unorganized mass of parenchymal cells that forms naturally at the site of wounds in plant tissues, and which is commonly artificially induced to form in plant as a means of initiating somatic embryogenesis.
A whose location on a chromosome is with a particular , and which is therefore suspected of causing or contributing to the phenotype. Candidate genes are often selected for study based on a priori knowledge or speculation about their functional relevance to the trait or disease being researched.
See '.
Any of a class of organic compounds having the generic chemical formula, and one of several major classes of found universally in biological systems. Carbohydrates include individual as well as larger and, in which multiple monosaccharide monomers are joined by. Abundant and ubiquitous, these compounds are involved in numerous essential biochemical processes and ; they are widely used as an energy source for cellular, as a form of energy storage, as molecules, and as to the activity of other molecules. Carbohydrates are often colloquially described as "sugars"; the prefix glyco- indicates a compound or process containing or involving carbohydrates, and the suffix -ose usually signifies that a compound is a carbohydrate or a derivative.
See '.
1. A that functions as a, binding to a solute and facilitating its movement across the membrane by undergoing a series of.
2. A protein to which a specific or has been conjugated and which thereby carries an capable of eliciting an response.
3. A protein which is included in an at high concentrations in order to prevent non-specific interactions of the assay's reagents with vessel surfaces, sample components, or other reagents. For example, in many techniques, albumin is intentionally allowed to bind non-specifically to the blotted membrane prior to, so as to "block" potential off-target binding of the to the membrane, which might otherwise cause background fluorescence that obscures genuine signal from the target.
A pre-existing nucleic acid sequence or construct, especially a DNA with an annotated sequence and precisely positioned, into which one or more can be readily or recombined by various methods. Recombinant vectors containing reliable,, and antibiotic resistance genes are commercially manufactured as cassettes to allow scientists to easily swap into and out of an active "slot" or locus within the plasmid. See also '.
Any reaction or process involving the decomposition of large or complex substances into smaller, simpler compounds, especially the breakdown of organic compounds in order to liberate energy. Catabolic processes and are usually exergonic and tend to involve oxidative steps that break chemical bonds, generating low-enthalpy, high-entropy products. Contrast '.
Any product of or of a catabolic pathway. See also '.
An increase in the reaction rate of a chemical reaction due to the presence of a. A reaction whose rate is increased in this manner is said to be catalyzed. -directed catalysis is the primary means by which many otherwise energetically unfavorable biochemical reactions occur.
Any chemical species or substance whose presence of one or more particular chemical reactions but which is itself unchanged by the reaction, being neither a reactant nor a product of the reaction. Catalysts often need only be present in very low concentrations relative to the reactants in order for catalysis to occur. They may be simple molecules which catalyze reactions spontaneously, though most biochemical reactions are catalyzed by specifically evolved which allow them to proceed at rates millions or billions of times faster than they otherwise would.
A highly DNA sequence located approximately 75 base pairs of the for many eukaryotic genes.
See '.
The basic structural and functional unit of which all living organisms are composed, essentially a self-replicating ball of surrounded by a which separates the interior from the external environment, thus providing a protected space in which the carefully controlled chemical reactions necessary to sustain biological processes can be carried out unperturbed. organisms are composed of a single autonomous cell, whereas organisms consist of numerous cells cooperating together, with individual cells more or less specialized or to serve particular functions. Cells vary widely in size, shape, and substructure, particularly between and. The typical cell is microscopic, averaging 1 to 20 micrometres in diameter, though they may range in size from 0.1 μm to more than 20 centimetres in diameter for the eggs laid by some birds and reptiles, which are highly specialized single-celled ova.
The branch of biology that studies the structures, functions, processes, and properties of biological, the self-contained units of life common to all living organisms.
The subdivision of the interior of a into distinct, usually compartments, including the and , a defining feature of the Eukarya.
A specialized layer of proteins lining the inner face of the in most eukaryotic cells, composed primarily of and and usually 100–1000 nanometres thick, which functions as a modulator of membrane behavior and cell surface properties.
The process of determining the number of within a biological sample or by any of a variety of methods. Counting cells is an important aspect of used widely in research and clinical medicine. It is generally achieved by using a manual or digital to count the number of cells present in small fractions of a sample, and then extrapolating to estimate the total number present in the entire sample. The resulting quantification is typically expressed as a density or concentration, i.e. the number of cells per unit area or volume.
The process by which living cells are grown and maintained, or "cultured", under carefully controlled conditions, generally outside of their natural environment. Optimal growth conditions vary widely for different cell types but usually consist of a suitable vessel containing a specifically formulated or that supplies all of the nutrients essential for life plus any desirable growth factors and, permits gas exchange, and regulates the environment by maintaining consistent physico-chemical properties. Some cell types require a solid surface to which they can in order to reproduce, whereas others can be grown while floating freely in a liquid or gelatinous. Most cells have a genetically determined reproduction limit, but cells will divide indefinitely if provided with optimal conditions.
The separation of an individual into two by any process. Cell division generally occurs by a complex, carefully structured sequence of events involving the reorganization of the parent cell's internal contents, the physical of the and, and the even distribution of contents between the two resulting cells, so that each ultimately contains approximately half of the original cell's starting material. It usually implies reproduction via the of the parent cell's genetic material prior to division, though cells may also divide without replicating their DNA. In prokaryotic cells, is the primary form of cell division. In eukaryotic cells, asexual division occurs by and, while specific cell types reserved for sexual reproduction can additionally divide by.
The merging or coalescence of two or more cells into a single cell, as occurs in the fusion of to form a. Generally this occurs by the destabilization of each cell's and the formation of bridges between them which then expand until the two cytoplasms are completely mixed; intercellular structures or such as may or may not fuse as well. Some cells can be artificially induced to fuse with each other by treating them with a fusogen such as polyethylene glycol or by passing an electric current through them.
A population of ' that is descended from a single primary culture through one or more generations or subcultures. All of the cells of an established cell line are genetically identical both within and across generations, and tend to share the same patterns of when cultured in similar conditions. Established lines that are also can be propagated indefinitely with little or no.
The selectively permeable surrounding all prokaryotic and eukaryotic cells, defining the outermost boundary of the cell and physically separating the from the environment. Like all membranes, the cell membrane is a flexible, fluid, sheet-like with,, and numerous other molecules embedded within or interacting with it from both sides. Embedded molecules often have alongside the membrane's lipids. Though the cell membrane can be freely crossed by many ions, small organic molecules, and water, most other substances require through special pores or or by or in order to enter or exit the cell, especially very large or electrically charged molecules such as proteins and nucleic acids. Besides regulating the transport of substances into and out of the cell, the cell membrane creates an organized interior space in which to perform life-sustaining activities and plays fundamental roles in all of the cell's interactions with its environment, making it important in,, defense, and, among numerous other processes.
The study of the various biological activities and biochemical processes which sustain life inside, particularly those related to and energy transfer, growth and, and the ordinary processes of the.
The spatial variation within a, i.e. the existence of differences in shape, structure, or function between different parts of the same cell. Almost all exhibit some form of polarity, often along an invisible axis which defines opposing sides or poles where the variation is most extreme. Having internal polarity permits cells to accomplish specialized functions such as or to serve as cells which must perform different tasks on different sides, or facilitates or.
The diverse set of processes by which cells transmit information to and receive information from themselves, from other cells, or from their surroundings. occurs in all cell types, prokaryotic and eukaryotic, and is of critical importance to the cell's ability to navigate and survive its physical environment. Countless mechanisms of signaling have evolved in different organisms and are often categorized according to the proximity between sender and recipient.
Any of a class of proteins embedded within or attached to the external surface of the, with one or more facing the environment and one or more that couple the binding of a particular to an event or process. Cell surface receptors are a primary means by which environmental signals are received by the cell and across the membrane into the cell interior. Some may also bind exogenous ligands and transport them into the cell in a process known as.
A tough, variously flexible or rigid layer of or polymers surrounding some cell types immediately outside of the, including plant cells and most, which functions as an additional protective and selective barrier and gives the cell a definite shape and structural support. The chemical composition of the cell wall varies widely between taxonomic groups, and even between different stages of the : in land plants it consists primarily of cellulose, hemicellulose, and pectin, while algae make use of carrageenan and agar, fungi use chitin, and bacterial cell walls contain.
Any molecule that exists outside of a or, freely floating in an such as blood plasma.
Of, relating to, consisting of, produced by, or resembling a or cells.
See '.
A class of immune response that does not rely on the production of but rather the activation of specific such as or cytotoxic T-lymphocytes, or the secretion of various from cells, in response to an.
Any apparently random variability observed in quantities measured in cell biology, particularly those pertaining to levels.
The conversion of a terminally from one -specific cell type to another. This involves to a state; an example is the conversion of mouse to an undifferentiated embryonic state, which relies on the Oct4, Sox2, Myc, and Klf4.
A unit for measuring defined as the distance between chromosomal for which the expected average number of intervening in a single generation is 0.01. Though not an actual measure of physical distance, it is used to infer the actual distance between two loci based on the apparent likelihood of a crossover occurring between them in any given division.
A generalized framework for understanding the flow of genetic information between macromolecules within biological systems. The central dogma outlines the fundamental principle that the sequence information encoded in the three major classes of biopolymer—,, and —can only be transferred between these three classes in certain ways, and not in others: specifically, information transfer between the and from nucleic acid to protein is possible, but transfer from protein to protein, or from protein back to either type of nucleic acid, is impossible and does not occur naturally.
A cylindrical composed of, present only in certain eukaryotes. A pair of centrioles migrate to and define the two opposite poles of a where, as part of a, they initiate the growth of the.
A specialized DNA sequence within a that links a pair of. The primary function of the centromere is to act as the site of assembly for, protein complexes which direct the attachment of to the centromere and facilitate of the chromatids during or.
The proportion of the total length of a encompassed by its, typically expressed as a percentage; e.g. a chromosome with a centromeric index of 15 is, with a short arm comprising only 15% of its overall length.
See '.
A type of whose shape forms an aqueous pore in a, permitting the passage of specific solutes, often small ions, across the membrane in either or both directions.
A set of axioms which state that, in the of any chromosome, species, or organism, the total number of will be approximately equal to the total number of residues, and the number of residues will be equal to the number of residues; accordingly, the total number of will equal the total number of . These observations illustrate the highly specific nature of the that occurs in all DNA molecules: even though non-standard pairings are technically possible, they are exceptionally rare because the standard ones are strongly favored in most conditions. Still, the 1:1 equivalence is seldom exact, since at any given time nucleobase ratios are inevitably distorted to some small degree by , missing bases, and non-canonical bases. The presence of polymers also alters the proportions, as an individual may contain any number of any of the bases.
A to which an has been attached; i.e. an. lack amino acids.
See '.
A non-directional, random change in the movement of a molecule, cell, or organism in response to a chemical stimulus, e.g. a change in speed resulting from exposure to a particular chemical compound.
A directed, non-random change in the movement of a molecule, cell, or organism in response to a chemical stimulus, e.g. towards or away from an area with a high concentration of a particular chemical compound.
A cross-shaped junction that forms the physical point of contact between two non-sister belonging to during. As well as ensuring proper of the chromosomes, these junctions are also the at which may occur during or, which results in the reciprocal exchange of DNA between the synapsed chromatids.
The presence of two or more populations of cells with distinct in an individual organism, known as a chimera, which has developed from the fusion of cells originating from separate ; each population of cells retains its own genome, such that the organism as a whole is a mixture of genetically non-identical tissues. Genetic chimerism may be inherited or acquired after birth ; in plants, it can result from grafting or errors in cell division. It is similar to but distinct from.
A type of small, lens-shaped found in the cells of green algae and plants which contains light-sensitive photosynthetic pigments and in which the series of biochemical reactions that comprise photosynthesis takes place. Like, chloroplasts are bound by a double membrane, contain their own from which they direct transcription of a unique set of genes, and replicate independently of the nuclear genome.
The set of molecules contained within, a type of photosynthetic located within the cells of some eukaryotes such as plants and algae, representing a semi-autonomous separate from that within the cell's nucleus. Like other types of plastid DNA, cpDNA usually exists in the form of small circular.
A chemical compound that is the principal sterol biosynthesized by animal cells and an essential component of, in which it serves to buffer the membrane's and plays roles in. It is produced primarily in tissues of the liver and the nervous system, and is transported in an esterified form by in the blood plasma.
The complete set of or of within a cell, tissue, organism, or species.
One copy of a newly copied, which is joined to the original chromosome by a. Paired copies of the same individual chromosome are known as.
A complex of,, and found in eukaryotic cells that is the primary substance comprising. Chromatin functions as a means of very long DNA molecules into highly organized and densely compacted shapes, which prevents the strands from becoming tangled, reinforces the DNA during, helps to prevent DNA damage, and plays an important role in regulating and.
A central amorphous mass of found in the nuclei of cells of the salivary glands in Drosophila larvae and resulting from the fusion of regions surrounding the of the somatically paired chromosomes, with the distal arms radiating outward.
A region of a that has been locally compacted or into, conspicuous under a microscope as a "bead", node, or dark-staining band, especially when contrasted with nearby uncompacted strings of DNA.
contained in, as opposed to. The term is generally used synonymously with.
The of an entire, as opposed to a segment of a chromosome or an.
A molecule containing part or all of the genetic material of an organism. Chromosomes may be considered a sort of molecular "package" for carrying DNA within the of cells and, in most eukaryotes, are composed of long strands of DNA coiled with which bind to and the strands to prevent them from becoming an unmanageable tangle. Chromosomes are most easily distinguished and studied in their completely condensed forms, which only occur during. Some simple organisms have only one chromosome made of circular DNA, while most eukaryotes have multiple chromosomes made of linear DNA.
The process by which eukaryotic chromosomes become shorter, thicker, denser, and more conspicuous under a microscope during due to systemic coiling and of strands of DNA in preparation for.
The process by which or separate from each other and migrate to opposite sides of the dividing cell during or.
See '.
A slender, thread-like, projection extending from the surface of a eukaryotic cell, longer than a but shorter than a. Most eukaryotic cells have at least one primary cilium serving sensory or signaling functions; some cells employ thousands of motile cilia covering their entire surface in order to achieve locomotion or to move extracellular material past the cell.
Any molecule, or, which forms a continuous closed loop without ends; e.g. bacterial chromosomes, and, as well as many other varieties of, including and some viral DNA. Contrast '.
Any fragments derived from tumor cells which are circulating freely in the bloodstream.
On the same side; adjacent to; from the same molecule. Contrast '.
Affecting a or sequence on the same nucleic acid molecule. A or sequence within a particular DNA molecule such as a is said to be cis-acting if it influences or acts upon other sequences located within short distances on the same molecule or chromosome; or, in the broadest sense, if it influences or acts upon other sequences located anywhere on the same chromosome of a. Cis-acting factors are often involved in the of by acting to inhibit or to facilitate. Contrast '.
A occurring within a which alters the functioning of a nearby or genes on the same. Cis-dominant mutations affect the of genes because they occur at sites that control transcription rather than within the genes themselves.
Any sequence or region of which the of nearby , typically by serving as a binding site for one or more. Contrast '.
Any of a class of flattened, membrane-bound or of the and and the. By traveling through one or more cisternae, each of which contains a distinct set of enzymes, newly created proteins and polysaccharides undergo chemical modifications such as and, which are used as packaging signals to direct their transport to specific destinations within the cell.
The branch of based solely on observation of the visible results of reproductive acts, as opposed to that made possible by the modern techniques and methodologies of. Contrast '.
1. The physical separation of a into multiple individual.
2. In, the series of divisions by which a is divided, without an accompanying overall change in size, into a ball of smaller cells constituting the early.
A trough-like indentation in the surface of the, often conspicuous when viewed through a microscope, that initiates the of the cytoplasm as the begins to narrow during.
The process of producing, either naturally or artificially, individual organisms or cells which are genetically identical to each other. Clones are the result of all forms of asexual reproduction, and cells that undergo produce daughter cells that are clones of the parent cell and of each other. Cloning may also refer to biotechnology methods which artificially create copies of organisms or cells, or, in, copies of DNA fragments or other molecules.
See '.
A type of that increases the of one or more genes by binding to an.
The strand of a double-stranded DNA molecule whose nucleotide sequence corresponds directly to that of the RNA transcript produced during . Though it is not itself transcribed, the coding strand is by convention the strand used when displaying a DNA sequence because of the direct analogy between its sequence and the of the RNA product. Contrast '; see also '.
A series of three consecutive in a coding region of a sequence. Each of these triplets codes for a particular or during. and molecules are each written in a language using four "letters", but the language used to construct proteins includes 20 "letters". Codons provide the key that allows these two languages to be into each other. In general, each codon corresponds to a single amino acid. The full set of codons is called the.
The preferential use of a particular to code for a particular rather than alternative codons that are synonymous for the same amino acid, as evidenced by differences between organisms in the frequencies of the synonymous codons occurring in their coding DNA. Because the is, most amino acids can be specified by multiple codons. Nevertheless, certain codons tend to be overrepresented in different species.
A mass of bounded by a and resulting from continuous cytoplasmic growth and repeated nuclear division without, found in some species of algae and fungi, e.g. Vaucheria and Physarum.
A relatively small, independent which associates with a specific and participates in the reaction catalyzed by the enzyme, often by forming a covalent bond with the. Examples include biotin,, and.
A derived from pantothenic acid that functions as a substrate for a wide range of in all living organisms and is notable for its role as a carrier of acyl groups which attach to its terminal sulphydryl group via a thioester bond. Its form, known as, is particularly important to numerous metabolic pathways, both and, including the synthesis and oxidation of and the oxidation of as part of the.
Any non-protein organic compound capable of binding to or interacting with an. Cofactors are required for the initiation of.
A property of biopolymers whereby two polymeric chains or "" aligned to each other will tend to form consisting of hydrogen bonds between the individual comprising each chain, with each type of nucleobase pairing almost exclusively with one other type of nucleobase; e.g. in molecules, pairs only with and pairs only with. Strands that are paired in such a way, and the bases themselves, are said to be complementary. The degree of complementarity between two strands strongly influences the stability of the molecule; certain sequences may also be internally complementary, which can result in a single strand. Complementarity is fundamental to the mechanisms governing,, and.
that is synthesized from a single-stranded template in a reaction catalyzed by the enzyme. cDNA is produced both naturally by retroviruses and artificially in certain laboratory techniques, particularly. In, the term may also be used to refer to the sequence of an mRNA transcript expressed as its DNA counterpart.
See '.
The controlled, inducible of a, either ' or '.
In, a measure of the proportion of the surface area of a that is covered by, commonly expressed as a percentage. A culture in which the entire surface is completely covered by a continuous, such that all cells are immediately adjacent to and in direct physical contact with other cells, with no gaps or voids, is said to be 100-percent confluent. Different may exhibit differences in morphology, growth rate, or depending on the degree of confluence. Because of, most show a significant reduction in the rate of as they approach complete confluence, though some may continue to divide, expanding vertically rather than horizontally by stacking themselves on top of the, until all available nutrients are depleted.
The three-dimensional spatial configuration of the atoms comprising a molecule or structure. The conformation of a is the physical shape into which its chains arrange themselves during, which is not necessarily rigid and may with the protein's particular chemical environment.
A change in the spatial or physical shape of a molecule or macromolecule such as a protein or nucleic acid, rarely spontaneously but more commonly as a result of some alteration in the molecule's chemical environment or an interaction with another molecule. Changes in the of proteins can affect whether or how strongly they bind or ; inducing these changes is a common means of activating, inactivating, or otherwise controlling the function of many enzymes and receptor proteins.
The movement of chromosomes to the during the and stages of.
A calculated order of the most frequent found at each position in a common and obtained by comparing multiple closely related sequence alignments.
A hypothetical mode of in which the two parental of the original molecule ultimately remain hybridized to each other at the end of the replication process, with the two daughter strands forming their own separate molecule; hence one molecule is composed of both of the starting strands while the other is composed of the two newly synthesized strands. This is in contrast to, in which each molecule is a hybrid of one old and one new strand. See also '.
A or sequence that is highly similar or identical across many species or within a, indicating that it has remained relatively unchanged through a long period of evolutionary time.
1. The continuous of a, as opposed to, in which a gene is only transcribed as needed. A gene that is transcribed continuously is called a constitutive gene.
2. A gene whose expression depends only on the efficiency of its in binding, and not on any or other which might or its transcription.
In, the phenomenon by which most normal eukaryotic cells cease to grow and upon reaching a critical cell density, usually as they approach full or come into physical contact with other cells. As a result, many types of cells cultured on plates or in will continue to proliferate until they cover the whole surface of the culture vessel, at which point the rate of cell division abruptly decreases or is arrested entirely, thus forming a confluent with minimal overlap between neighboring cells, even if the nutrient medium remains plentiful, rather than stacking themselves on top of each other. or cells tend not to respond to cell density in the same way and may continue to proliferate at high densities. This type of density-dependent inhibition of growth is similar to and may occur simultaneously with, but is nonetheless distinct from, the related phenomenon of contact inhibition of movement, whereby moving cells respond to physical contact by temporarily stopping and then reversing their direction of locomotion away from the point of contact.
A continuous sequence of generated by assembling cloned fragments by means of their overlapping sequences.
A phenomenon observed in some,, and which have multiple, whereby the binding of a to one or more sites apparently increases or decreases the affinity of one or more other binding sites for other ligands. This concept highlights the sensitive nature of the chemistry that governs interactions between biomolecules: the strength and specificity of interactions between protein and ligand are influenced, sometimes substantially, by nearby interactions and by the local chemical environment in general. Cooperativity is frequently invoked to account for the non-linearity of data resulting from attempts to measure the association/dissociation constants of particular.
See '.
A resulting from a mistake made during.
A phenomenon in which sections of a are repeated and the number of varies between individuals in the population, usually as a result of or events that affect entire genes or sections of chromosomes. Copy-number variations play an important role in generating within a population.
A protein that works together with one or more to regulate.
A type of that reduces the of one or more genes by binding to and activating a.
See '.
A region of a in which occur or with high frequency.
A sequence of DNA in which a nucleotide is immediately followed by a nucleotide on the same in the 5'-to-3' ; the "p" in CpG refers simply to the intervening group linking the two consecutive nucleotides.
Any of numerous folds or in the inner membrane, which give this membrane its characteristic wrinkled shape and increase the surface area across which and supporting reactions can occur. Cristae are studded with proteins such as ATP synthase and various cytochromes.
See '.
Any chemical bond or series of bonds, normal or abnormal, natural or artificial, that connects two or more molecules to each other, creating an even larger, often structurally rigid and mechanically durable complex. Crosslinks may consist of covalent, ionic, or intermolecular interactions, or even extensive physical entanglements of molecules, and may be reversible or irreversible; in polymer chemistry the term is often used to describe macrostructures that form predictably in the presence of a specific catalyst. In the usage generally implies abnormal bonding between different which are ordinarily separate, especially and. Crosslinking of DNA may occur between on opposite of a molecule, or between bases on the same strand, via the formation of covalent bonds that are stronger than the hydrogen bonds of normal ; these are common targets of pathways. Proteins are also susceptible to becoming crosslinked to DNA or to other proteins through bonds to specific surface residues, a process which is deliberately induced in many laboratory methods such as and which can be useful for studying in their. Crosslinks are generated by a variety of and agents, including chemical compounds and high-energy radiation, and tend to interfere with normal cellular processes such as and, meaning their persistence usually compromises cell health.
1. An abbreviation of.
2. An abbreviation of.
The end of a linear chain of that is terminated by the free carboxyl group of the last amino acid to be added to the chain during. This amino acid is said to be C-terminal. By convention, sequences, domains, active sites, or any other structure positioned nearer to the C-terminus of the or the folded it forms relative to others are described as. Contrast '.
The total amount of contained within a of a particular organism or species, expressed in number of or in units of mass ; or, equivalently, one-half the amount in a . For simple diploid the term is often used interchangeably with, but in certain cases, e.g. in hybrid descended from parents of different species, the C-value may actually represent two or more distinct contained within the same nucleus. C-values apply only to, and notably exclude.
A term used to describe a diverse variety of questions regarding the immense variation in nuclear or among eukaryotic species, in particular the observation that genome size does not correlate with the perceived complexity of organisms, nor necessarily with the number of they possess; for example, many single-celled protists have genomes containing thousands of times more DNA than the human genome. This was considered paradoxical until the discovery that eukaryotic genomes consist mostly of, which lacks genes by definition. The focus of the enigma has since shifted to understanding why and how eukaryotic genomes came to be filled with so much non-coding DNA, and why some genomes have a higher gene content than others.
See '.
One of the four standard used in molecules, consisting of a with its N9 nitrogen to the C1 carbon of a sugar. Cytosine bonded to is known as, which is the version used in.
The branch of involving the detection and identification of various cellular structures and components, in particular their, using techniques of biochemical analysis and visualization such as chemical and, spectrophotometry and spectroscopy, radioautography, and electron microscopy.
The branch of that studies how influence and relate to cell behavior and function, particularly during and.
Any of a broad and loosely defined class of small and which have functions in , typically by interacting with specific.
The final stage of in both and, usually immediately following the division of the, during which the of the parent cell is and divided approximately evenly between two. In animal cells, this process occurs by the closing of a microfilament in the equatorial region of the dividing cell. Contrast '.
The study of the morphology, processes, and life history of living, particularly by means of light and electron microscopy. The term is also sometimes used as a synonym for the broader field of.
See '.
The interdisciplinary field that studies,, and at the level of an individual cell by making use of single-cell molecular techniques and advanced microscopy to visualize the interactions of cellular components .
All of the material contained within a excluding the ; i.e. that part of the which is enclosed by the but separated from the by the, consisting of the fluid and the totality of its contents, including all of the cell's internal,, and substructures such as,, the, and, and a network of filamentous known as the. Some definitions of cytoplasm exclude certain organelles such as and. Composed of about 80 percent water, the numerous small molecules and macromolecular complexes dissolved or suspended within the cytoplasm give it characteristic viscoelastic and thixotropic properties, allowing it to behave variously as a gel or a liquid solution. Though continuous throughout the intracellular space, the cytoplasm can often be resolved into distinct phases of different density and composition, such as an and. Most of the metabolic and biosynthetic activities of the cell take place in the cytoplasm, including by. Despite their physical separation, the cytoplasm and the nucleus are mutually dependent upon each other, such that an isolated nucleus without cytoplasm is as incapable of surviving for long periods as is the.
The flow of the inside a cell, driven by forces exerted upon cytoplasmic fluids by the. This flow functions partly to speed up the transport of molecules and suspended in the cytoplasm to different parts of the cell, which would otherwise have to rely on passive diffusion for movement. It is most commonly observed in very large eukaryotic cells, for which there is a greater need for transport efficiency.
An eukaryotic cell; or all other cellular components besides the nucleus considered collectively. The term is most often used in the context of experiments, during which the cytoplast can sometimes remain viable in the absence of a nucleus for up to 48 hours.
A used as one of the four standard nucleobases in both and molecules. Cytosine forms a with.
The soluble aqueous phase of the, in which small particles such as,,, and many other molecules are suspended or dissolved, excluding larger structures and such as,,, and the.
D
A resulting from the of an initial progenitor, known as the. Generally two daughter cells are produced per division.
An unsupervised algorithm that estimates an activity score for a pathway in a gene expression matrix, following a denoising step.
A spontaneous in the genome of an individual organism that is new to that organism's lineage, having first appeared in a of one of the organism's parents or in the fertilized egg that develops into the organism; i.e. a mutation that was not present in either parent's genome.
The assembly of a synthetic from free without relying on an existing, i.e. de novo, by any of a variety of laboratory methods. De novo synthesis makes it theoretically possible to construct completely with no naturally occurring equivalent, and no restrictions on size or sequence. It is performed routinely in the commercial production of customized, made-to-order sequences such as.
The removal of an acetyl group from a chemical compound, protein, or other biomolecule via hydrolysis of the covalent ester bond adhering it, either spontaneously or by catalysis. Deacetylation is the opposite of.
The redundancy of the, exhibited as the multiplicity of different that specify the same. For example, in the, the amino acid serine is specified by six unique codons. Codon degeneracy accounts for the existence of.
The release of the contents of a secretory granule into an space by the of the granule with the cell's plasma membrane.
A type of in which one or more are removed from a.
The removal of a methyl group from a chemical compound, protein, or other biomolecule, either spontaneously or by catalysis. Demethylation is the opposite of ; both reactions play important roles in numerous biochemical processes, including in, as the methylation state of particular residues within particular proteins or nucleic acids can affect their structural in a way that alters their affinity for other molecules, making transcription at nearby genetic loci more or less likely.
The process by which or lose their,, and/or, either reversibly or irreversibly, through the application of some external chemical or mechanical stress, e.g. by heating, agitation, or exposure to a strong acid or base, all of which can disrupt intermolecular forces such as hydrogen bonding and thereby change or destroy chemical activity. Denatured proteins may be both a cause and a consequence of cell death. Denaturation may also be a normal process; the denaturation of molecules, for example, which breaks the hydrogen bonds between and causes the separation of the duplex molecule into two, is a necessary step in and and hence is routinely performed by enzymes such as. The same mechanism is also fundamental to laboratory methods such as.
One of the four standard used in molecules, consisting of an with its N9 nitrogen to the C1 carbon of a sugar. Adenine bonded to forms an alternate compound known simply as, which is used in.
One of the four standard used in molecules, consisting of a with its N9 nitrogen to the C1 carbon of a sugar. Cytosine bonded to forms an alternate compound known simply as, which is used in.
One of the four standard used in molecules, consisting of a with its N9 nitrogen to the C1 carbon of a sugar. Guanine bonded to forms an alternate compound known simply as, which is used in.
Any of a class of enzymes which catalyze the hydrolytic cleavage of in molecules, thereby severing of and causing the degradation of DNA polymers into smaller components. Compare '.
A molecule composed of a series of covalently linked, each of which incorporates one of four : , , , and . DNA is most often found in form, which consists of two, nucleotide chains in which each of the nucleobases on each individual is via hydrogen bonding with one on the opposite strand; this structure commonly assumes the shape of a. DNA can also exist in form. By storing and encoding genetic information in the of these nucleobases, DNA serves as the universal molecular basis of biological inheritance and the fundamental template from which all proteins, cells, and living organisms are constructed.
A containing as its sugar component, and the or subunit used to build molecules. Deoxyribonucleotides canonically incorporate any of four : , , , and . Compare '.
A sugar derived from by the replacement of the hydroxyl group attached to the C2 carbon with a single hydrogen atom. D-deoxyribose, in its cyclic ring form, is one of three main functional groups of and hence of molecules.
See '.
The removal of a group,, from a chemical compound, protein, or other biomolecule, either spontaneously or by catalysis. Dephosphorylation is the opposite of ; both reactions are common molecular modifications involved in numerous biochemical pathways and processes, including in metabolism, where high-energy bonds to phosphate groups are used to transfer energy between molecules, and in the of proteins, where the phosphorylation state of particular residues can affect the protein's affinity for other molecules or function as a.
The spontaneous loss of one or more from a or molecule, either or, via the hydrolytic cleavage of the linking base and sugar, releasing a free purine nucleobase and a. are especially prone to depurination. Loss of bases can also occur spontaneously but is far less common.
The artificial modification of a molecule or protein with the intent of altering its solubility or other chemical properties so as to enable analysis, or of it by attaching a detectable chemical moiety to make it easier to identify and track '. Molecules modified in this way are described as derivatives of their naturally occurring counterparts and are said to have been derivatized.
A specialized cell junction between neighboring cells consisting of a network of keratin filaments and structural proteins bridging the gap between the plasma membranes.
The failure of that have normally during to remain paired during. Desynapsis is usually caused by the improper formation of. Contrast '.
The branch of biology that studies the various processes and phenomena by which organisms grow and develop into mature forms capable of reproduction. In the broadest sense the field may encompass topics such as sexual and asexual reproduction, and sporogenesis,, embryogenesis, the renewal and of into specialized cell types, birth or hatching, metamorphosis, and the regeneration of mature tissues.
In, the fifth and final substage of, following and preceding. During diakinesis, the chromosomes are further condensed, the two reach opposite poles of the cell, and the begins to extend from the poles to the equator.
Having two instead of the normal one.
The process by which a eukaryotic cell changes from one to another, in particular from a non-specialized to a more specialized cell type which is then said to be differentiated. This usually occurs by a carefully regulated series of modifications which change the specific set of by the cell, turning certain genes "off" and others "on". These modifications result in a cascade of changes which can dramatically alter the cell's size, shape,, properties, and rate of, and therefore its functions, behaviors, and responsiveness to signals, permitting multicellular organisms to create a huge variety of functionally distinct cell types from a single. Differentiation occurs repeatedly during an organism's development from a single-celled into a complex multicellular system of and cell types, and continues to some extent after the organism reaches maturity in order to repair and replace damaged and dying cells. In most cases differentiation is irreversible, though some cells may also undergo in specific circumstances.
A molecular aggregate consisting of two. The term is often used to describe a composed of two proteins, either the same protein or different proteins ; or to an individual protein composed of two. Compare ', ', and '.
A molecular consisting of exactly two covalently linked ; or any two nucleotides which are immediately adjacent to each other on the same of a longer polymer.
Having two copies of each. Contrast ' and '.
In, the fourth of the five substages of, following and preceding. During diplonema, the disassembles and the paired begin to separate from one another, though they remain tightly bound at the where has occurred.
Any two or more of a specific occurring in the same orientation and on the same, either separated by intervening nucleotides or not. An example is the sequence, in which occurs twice, though separated by six nucleotides that are not part of the repeated sequence. A direct repeat in which the repeats are immediately adjacent to each other is known as a.
The end-to-end orientation of a linear or of a polymer or a. The nomenclature used to indicate nucleic acid directionality is based on the chemical convention of identifying individual carbon atoms in the or sugars of nucleotides, specifically the and of the ring. The sequence of nucleotides in a polymeric chain may be read or interpreted in the 5'-to-3' direction or in the opposite 3'-to-5' direction. Most types of nucleic acid synthesis, including and, build chains of nucleotides exclusively in the 5'-to-3' direction, because the involved can only catalyze the addition of free nucleotides to the open 3'-end of the previous nucleotide in the chain. Because of this, the convention when writing any nucleic acid sequence is to present it in the 5'-to-3' direction from left to right. In nucleic acids, the two paired strands must be in order to with each other. Polypeptide directionality is similarly based on identifying the functional groups of, specifically the amino group, which forms the, and the carboxyl group, which forms the ; amino acid sequences are assembled in the N-to-C direction during, and by convention are written in the same direction.
A composed of two joined by a covalent. See also ' and '.
A hypothetical mode of in which the pairing of and newly synthesized strands is not consistent within the same daughter molecule; i.e. each of the replicated daughter molecules is a heterogeneous mixture, with some segments composed of the original template strands and others composed of the newly synthesized strands. This process implies that the pairing of strands does not occur uniformly at all. Only the mode of replication occurs naturally. See also '.
Any exergonic process of microbial by which redox-active chemical species participate in oxidation-reduction reactions to provide the cell with energy needed for sustaining activities. substances are absorbed by the cell from its environment and then decomposed to release energy, with the subsequently out of the cell. This is in contrast to an, in which the atoms of the exogenous substances are reused in the synthesis of biomolecules or the fabrication of cellular components.
Any quantity used to measure the dissimilarity between the levels of different.
See '.
A method of taxonomic identification in which short DNA sequences from one or more specific genes are isolated from unidentified samples and then with a genomic in order to uniquely identify the species or other taxon from which the samples originated. The sequences used in the comparison are chosen carefully from genes that are both widely and that show greater between species than within species, e.g. the cytochrome c oxidase gene for eukaryotes or certain genes for prokaryotes. These genes are present in nearly all living organisms but tend to evolve different mutations in different species, such that a unique sequence variant can often be linked to one particular species, effectively creating a unique identifier akin to a retail barcode. DNA barcoding allows unknown specimens to be identified from otherwise indistinct tissues or body parts, where identification by morphology would be difficult or impossible, and the library of organismal barcodes is now comprehensive enough that even organisms previously unknown to science can often be classified with confidence. The simultaneous identification of multiple different species from a mixed sample is known as metabarcoding.
The process of compacting very long molecules into densely packed, orderly configurations such as, either ' or '.
A technology used to measure levels of transcripts or to detect certain changes in. It consists of an array of thousands of microscopic spots of , called features, each containing picomoles of a specific DNA sequence. This can be a short section of a or any other DNA element, and is used as a to hybridize a, cRNA, or sample under conditions. Probe-target is usually detected and quantified by fluorescence-based detection of targets.
Any of a class of which synthesize molecules from individual. DNA polymerases are essential for and usually work in pairs to create identical copies of the two of an original double-stranded molecule. They build long chains of DNA by adding nucleotides one at a time to the of a DNA strand, usually relying on the provided by the strand to copy the nucleotide sequence faithfully.
The set of processes by which a cell identifies and corrects structural damage or in the molecules that encode its. The ability of a cell to repair its DNA is vital to the integrity of the genome and the normal functionality of the organism.
The process by which a molecule copies itself, producing two identical copies of one original DNA molecule. This occurs by a involving the separation of a double-stranded molecule into two individual strands, each of which then serves as a template for the synthesis of a new strand of complementary nucleotides. Replication of takes place during the of, though molecules such as and may replicate independently at other times. DNA replication is the chief process by which genetic information is propagated in all living organisms and the central mechanism underlying biological inheritance.
The process of determining, by any of a variety of different methods and technologies, the order of the in the long chain of nucleotides that constitutes a of.
Any mechanism by which are exchanged non-reciprocally that causes continual fluctuations in the of DNA during an organism's lifetime. Such mechanisms are often major drivers of speciation between populations.
A protein containing at least one structural motif capable of recognizing and interacting with the of a or molecule. DNA-binding domains may bind to specific sequences or have a non-specific affinity for DNA. They are the primary functional components of, including many and regulatory proteins.
Any or containing one or more capable of interacting chemically with one or more parts of a molecule, and consequently having a specific or general affinity for and/or. DNA-binding activity often depends on the presence and physical accessibility of a specific nucleobase sequence, and mostly occurs at the, since it exposes more of the functional groups which uniquely identify the bases. Binding is also influenced by the spatial conformation of the DNA chain and the occupancy of other proteins near the binding site; many proteins cannot bind to DNA without first undergoing induced by interactions with other molecules.
See '.
A discrete, usually contiguous region of a which serves a particular function or is defined by particular physico-chemical properties, and especially one which folds independently of the rest of the polypeptide into a characteristic, self-stabilizing spatial as part of the protein's and which contributes to or defines its biological activity. Large proteins are generally composed of multiple domains linked by short, intervening non-domain sequences. Domains are commonly grouped into classes with similar properties or functions, e.g.. More broadly, the term may also be used to refer to a discrete structural entity within any biomolecule, including functionally or compositionally distinct subregions of and.
Any mechanism by which organisms neutralize the large difference in caused by the presence of differing numbers of in the different sexes, thereby equalizing the of sex-linked genes so that the members of each sex receive the same or similar amounts of the of such genes. An example is in female mammals.
The shape most commonly assumed by molecules, resembling a ladder that has been twisted upon its long axis, with the rungs of the ladder consisting of . This is the most energetically stable conformation of the double-stranded forms of both and under most naturally occurring conditions, arising as a consequence of the of the and the stacking of the bonded to it. In, the most common DNA variant found in nature, the double helix has a right-handed twist with about 10 base pairs per full turn, and the molecular geometry results in an alternating pattern of "grooves" of differing widths between the parallel backbones.
The loss of continuity of the in both strands of a molecule, in particular when the two breaks occur at sites that are directly across from or very close to each other on the complementary strands. Contrast '.
Composed of two, molecules or which are held together by hydrogen bonds between the complementary of each strand, known as. Compare '.
Any molecule that is composed of two, polymers, known as, which are bonded together by hydrogen bonds between the complementary. Though it is possible for DNA to exist as a, it is generally more stable and more common in double-stranded form. In most cases, the complementary causes the twin strands to coil around each other in the shape of a.
Any molecule that is composed of two, polymers, known as, which are bonded together by hydrogen bonds between the complementary. Though RNA usually occurs in, it is also capable of forming duplexes in the ; an example is an transcript pairing with an of the same transcript, which effectively the gene from which the mRNA was transcribed by preventing translation. As in dsDNA, the in dsRNA usually causes the twin strands to coil around each other in the shape of a.
Any process, natural or artificial, which decreases the level of of a certain. A gene which is observed to be expressed at relatively low levels in one sample compared to another sample is said to be downregulated. Contrast '.
Towards or closer to the of a chain of nucleotides, or to the of a chain. Contrast '.
See '.
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See '.
The production of a second copy of part or all of a or, either naturally or artificially, and the retention of both copies; especially when both the copy and the original sequence are retained ' within the same molecule, often but not necessarily to each other. See also ', ', and '.
See .
The abnormal growth or development of a or organ; a change in the growth, behavior, or organization of cells within a tissue, or the presence of cells of an abnormal type, such that the tissue becomes disordered, an event which often precedes the development of cancer.
E
A molecule exposed on the surface of a cell which effectively tags the cell for, inducing to engulf or "eat" it. The presence of oxidized or phosphatidylserine, or the absence of sialic acid from cell surface or, are all commonly used as eat-me signals in certain cell types. See also '.
Occurring or developing in an abnormal place or position or in an unusual form or manner; displaced, malpositioned, or produced in an unnatural context. For example, ectopic expression refers to the expression of a particular gene product in a cell or tissue where it is not normally expressed. Contrast '.
Any small molecule or which by interacting with a particular changes its catalytic activity but is not itself changed. A positive effector enhances the enzyme's activity while a negative effector reduces it.
The process by which electrons are transferred from electron donors to electron acceptors via a stepwise series of redox reactions carried out by dedicated and, especially as a component of which convert chemical energy from food into a form that is readily accessible by the cell. Most electron transport chains begin by oxidizing molecules derived from such as and, converting them into a series of intermediate compounds via a specific sequence of independently catalyzed reactions, with the products of the previous reaction used as reactants in the next reaction until ultimately reaching a terminal electron acceptor. The particular compounds used as donors, intermediates, and acceptors vary widely between organisms and cell types; in, the terminal acceptor is diatomic oxygen, whereas uses other acceptors. In all variants, the free energy released by these reactions is coupled to the pumping of protons across a membrane in order to generate an electrochemical gradient which is then used to drive the production of, a process known as. In eukaryotes, electron transport chains are conducted by proteins embedded within the membranes of and, while in prokaryotes the relevant proteins are embedded within the.
The physical separation of molecules, e.g. or, according to their movement through a fluid medium to which an electric field is applied, where the distance they travel is proportional to their size. Because of their negatively charged, nucleic acids are repelled by the negative electrode at one end of the medium and attracted to the positive electrode at the other end, which causes them to be pulled toward the latter over time; proteins and even whole cells may migrate through the medium in a similar manner. The speed at which the molecules migrate depends on their net electric charge and is inversely proportional to their overall size, such that very small molecules tend to move faster through the medium than very large molecules. Thus electrophoretic techniques, particularly with agarose or polyacrylamide-based gels as the supporting medium, are widely used in molecular biology laboratories to quickly and conveniently isolate molecules of interest from heterogeneous mixtures and/or identify them based on their expected molecular weight. Reference markers containing molecules of known weight are commonly run alongside unknown samples to aid size-based identification. Electrophoresis is often combined with other techniques such as.
A molecular biology technique in which a strong electric field is applied to living cells in order to temporarily increase the permeability of their cell membranes, allowing exogenous nucleic acids, proteins, or chemical compounds to easily pass through the membrane and thereby enter the cells. It is a common method of achieving and.
The linear growth of a polymer by the sequential addition of individual monomers to a , e.g. during or, especially when it occurs by with a. The term is often used to describe steps in certain laboratory techniques such as the.
A which, by binding to a, promotes of the chain during.
The developing organism that represents the earliest stages of in all sexually reproducing organisms, traditionally encompassing the period after of an egg cell and formation of the but prior to birth, hatching, or metamorphosis. During this period, known as embryonic development, the single-cell zygote is transformed by repeated and rearrangements into a series of increasingly complex multicellular structures. For humans, the term "embryo" is only used until the ninth week after conception, after which time the embryo is known as a foetus; for most other organisms, including plants, "embryo" can be used more broadly to describe any early stage of the life cycle.
The quality of genetic that results from a specific configuration of interacting, rather than simply their combination.
Any process by which a substance is uptaken by or brought inside of a, crossing the from an into an, which includes the subclasses of,, and processes. All of these involve surrounding an extracellular molecule, protein, or even another cell or organism with an extension or of the cell membrane, which then "buds off" or separates from the rest of the membrane on the cytoplasmic side, forming a membrane-enclosed containing the ingested materials. By this mechanism the material can cross the without being exposed to the hydrophobic space in between, instead remaining suspended in the fluid of the extracellular space. Many large, polar macromolecules which cannot simply diffuse across the membrane, such as and, are transported into the cell by endocytosis. It is distinguished from alternative routes such as passing through or being chaperoned by. The reverse process is called.
Originating or arising inside of an organism or cell; produced by the organism or cell itself, rather than sourced from the external environment; of or pertaining to native or internal factors or processes, to be distinguished from foreign or factors or processes.
Any surrounding an or, e.g. that of the,,,, , etc.
Any whose activity is to cleave within a chain of, including those that cleave relatively nonspecifically and those that cleave only at very specific sequences. When recognition of a specific sequence is required, endonucleases make their cuts in the middle of the sequence. Contrast '.
The irregular network of unit membranes, continuous with the, that extends from the into the in most eukaryotic cells, where it serves important packaging and transport functions for newly synthesized macromolecules. The membranes interweave to form a mesh of tubular channels and flattened sacs called which house a variety of enzymes that perform including proteins for. The outer surfaces of so-called are studded with attached that serve as sites of protein synthesis, whereas, lacking ribosomes, functions in the synthesis of and steroid hormones and in the detoxification of metabolic wastes. Generally both types of ER occur together, though some cell types are characterized by different proportions of rough and smooth ER, depending on the activities of the cell.
Any of a class of intracellular which serve transportation and sorting functions in eukaryotic cells as part of the. They are formed when proteins or other macromolecules enter the cytoplasm inside invaginated from the or the by, after which they are shuttled across the cell to various destinations; e.g. endosomes carrying foreign molecules often fuse with, where the contents are then degraded.
A region of DNA near a that can be bound by an to increase or by a to decrease expression.
A subclass of transcribed from regions of DNA containing sequences. The expression of a given eRNA generally correlates with the activity of the corresponding enhancer in enhancing transcription of its target genes, suggesting that eRNAs play an active role in gene regulation or.
Occurring or developing in the normal or natural place or position, as opposed to.
To artificially remove the from a, e.g. by micromanipulation in the laboratory or by destroying it through irradiation with ultraviolet light, rendering the cell.
A which acts as a for a biological process by accelerating a specific chemical reaction, typically by binding one or more molecules and decreasing the activation energy necessary for the initiation of a particular reaction involving the substrate. Enzymatic catalysis often results in the chemical conversion of the substrate into one or more products, which then inhibit or permit subsequent reactions. All consist of a series of individual reactions which each depend upon one or more specific enzymes to drive them forward at rates fast enough to sustain life.
A designed to detect the presence of a particular or in a liquid sample using conjugated to capable of specifically binding the antigen. The antigen of interest is usually first immobilized by adhering to a solid support, then one or more antigen-specific antibodies covalently bonded to a particular enzyme are added and any unbound antibody is washed away; when the attached enzyme's is subsequently added, the reaction between enzyme and substrate produces a detectable, quantifiable change in some measurable , thus reporting the presence of the targeted antigen in the sample. ELISA techniques are widely used as diagnostic tools in clinical medicine and academic research, as well as a form of quality control in many biotechnology industries.
1. Another name for a, especially one that is capable of integrating into a.
2. In eukaryotes, any non-integrated circular molecule that is stably maintained and replicated in the simultaneously with the rest of the host cell. Such molecules may include viral genomes, bacterial plasmids, and aberrant chromosomal fragments.
The collective action of multiple genes interacting during. A form of gene action, epistasis can be either additive or multiplicative in its effects on specific.
The specific site or region within an such as a or which is recognized by B or T cells of the immune system, against which a specific is produced, and with which the antibody's specifically interacts or binds. In proteins, epitopes are typically of 4–5 amino acid residues, sequential or discontiguous, which by virtue of the distinct spatial they adopt upon are able to uniquely interact with a particular paratope. In this sense they may be considered, though they do not necessarily overlap with ligand binding sites and need not be in any way relevant to the protein's normal function. Very large molecules may have multiple epitopes, each of which is recognized by a different antibody.
See '.
A relatively open, lightly compacted form of in which is only sporadically bound in and thus broadly accessible to binding and manipulation by and other molecules. Euchromatic regions of a genome are often enriched in and actively undergoing, in contrast to, which is relatively gene-poor, nucleosome-rich, and less accessible to transcription machinery.
The condition of a cell or organism having an abnormal number of complete sets of, possibly excluding the. Euploidy differs from, in which a cell or organism has an abnormal number of one or more specific individual chromosomes.
The change in the characteristics of biological populations over successive generations. In the most traditional sense, it occurs by changes in the frequencies of in a population's.
Occurring outside of a cell or organism, as with observations made or experiments performed in or on cells or which have been isolated or removed from their natural context to an external environment. This is in contrast to ' observations, which are made in an entirely natural context.
The enzymatic removal of a polynucleotide sequence from one or more strands of a, or of a polypeptide sequence from a, typically implying both the breaking of the polymeric molecule in two locations and the subsequent rejoining of the two breakpoints after the sequence between them has been removed. The term may be used to describe a wide variety of processes performed by distinct enzymes, including most and pathways.
Any process by which a substance is secreted from or transported out of a, crossing the from the into the, especially that which occurs by the fusion of the membrane surrounding a secretory with the larger cell membrane. This fusion causes the intra-vesicular space to merge with the extracellular fluid, releasing the vesicle's contents on the exterior side of the cell without exposing them to the hydrophobic space between the. More narrowly the term may refer in particular to the bulk transport of a large amount of molecules out of the cell all at once, often or which are too large and polar to passively diffuse across the membrane themselves. The reverse process, whereby materials are invaginated into the cell, is known as.
Originating outside of an organism or cell; of or pertaining to foreign or external factors or processes, to be distinguished from native or factors or processes.
The entire set of within a particular, including of mature mRNAs as well as.
Any part of a that encodes a part of the final mature produced by that gene after have been removed by. The term refers to both the sequence as it exists within a DNA molecule and to the corresponding sequence in RNA transcripts.
Any whose activity is to cleave within a chain of, including those that cleave only upon recognition of a specific sequence. Exonucleases make their cuts at either the or of the sequence.
1. An intracellular multi-protein complex which serves the function of degrading various types of molecules.
2. A type of membrane-bound produced in many eukaryotic cells by the inward budding of an and the subsequent fusion of the endosome with the, causing the release of the vesicle into various extracellular spaces, including biological fluids such as blood and saliva, where they may serve any of a wide variety of physiological functions, from waste management to intercellular signaling.
An intracellular multi-protein complex which serves the function of degrading various types of molecules.
A type of, usually a or viral vector, designed specifically for the of a in a target cell, rather than for some other purpose such as.
File:pET28a-T7-lacO-GFP.svg|thumb|right|350px|Plasmid map of a 3,756- ' used in the expression of a that makes green [fluorescent protein]. The vector also includes a gene for the lac'' repressor and a gene conferring resistance to the antibiotic kanamycin, as well as various for driving the expression of these genes.
Any part of an which is retained within a precursor, i.e. not excised by , and is therefore present in the mature, analogous to the of RNA transcripts. Contrast '.
See '.
Outside the of a or cells; i.e. located or occurring externally to a cell. Contrast '; see also '.
The network of interacting and minerals secreted by and existing outside of and between cells in structures such as and, forming a hydrated, mesh-like, semi-solid suspension which not only holds the cells together in an organized fashion but also provides structural and biochemical support, acting as an elastic, compressible buffer against external stresses as well as both regulating and influencing numerous aspects of cell behavior, among them,,,, and. The composition and properties of the ECM vary enormously between organisms and tissue types, but generally it takes the form of a gel in which various fibrous proteins, enzymes, and are embedded. Cells themselves both produce the matrix components and respond constantly to local matrix composition, a source of environmental feedback which is critical for, tissue organization, and development.
Any that is not found in or in the of a cell and hence is not. This may include the DNA contained in or such as or, or, in the broadest sense, DNA introduced by viral infection. Extrachromosomal DNA usually shows significant structural differences from nuclear DNA in the same organism.
F
A type of by which substances are conveyed across more quickly than would be possible by ordinary passive diffusion alone, generally because act as shuttles or pores, being arranged in such a way as to provide a environment that is favorable for the movement of small polar molecules, which would otherwise be repulsed by the interior of the.
The of a only as needed, as opposed to, in which a gene is transcribed continuously. A gene that is transcribed as needed is called a facultative gene.
Any of a subclass of compounds consisting of a carboxylic acid bonded to an aliphatic chain of hydrocarbons, usually 4 to 28 carbon atoms in length, which may be either saturated or unsaturated. In biological systems, fatty acid chains are commonly linked to other compounds via ester bonds, primarily in,, and derivatives of, all of which serve a wide variety of important cellular functions including as structural components of membranes and as energy sources in metabolic pathways.
Any in which organic molecules such as or other carbohydrates are in the absence of oxygen in order to produce ; or, in the broadest sense, any catabolic process in which organic compounds serve as both electron donors and acceptors. This definition distinguishes fermentation from, where inorganic diatomic oxygen is the terminal electron acceptor, and from some types of. Fermentation encompasses hundreds of different redox pathways which start and end with a huge variety of reactants and end-products, often branching from various steps in, with the most common fermentation products being lactate, acetate, ethanol, succinate, propionate, butyrate, carbon dioxide, and diatomic hydrogen. It occurs in both prokaryotes and eukaryotes in conditions where exogenously supplied electron acceptors are unavailable, especially in oxygen-poor environments. Fermentation yields the equivalent of just 2 to 5 ATP per molecule of glucose, making it much less efficient than aerobic respiration, which can yield as much as 32 ATP per molecule of glucose. In multicellular organisms that primarily rely on aerobic respiration, such as animals, it is often employed as a contingency pathway; the term anaerobic glycolysis refers to the diversion of glycolysis intermediates to fermentation pathways when tissues cannot keep up with the demand for ATP due to insufficient oxygen supply.
A molecule exposed on the surface of a cell destined for which is used to attract to engulf and eliminate the cell by. See also '.
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1. The preservation of biological material by treating it with a chemical that prevents or delays the natural postmortem processes of decay which would otherwise eventually cause cells, tissues, and biomolecules to lose their characteristic structures and properties. Biological specimens are usually fixed with the broad objective of arresting or slowing biochemical reactions for long enough to study them in detail, essentially 'freezing' cellular processes in their natural state at a specific point in time, while minimizing disruption to existing structures and arrangements, all of which can improve subsequent and microscopy of the fixed samples. Though fixation tends to irreversibly terminate any ongoing reactions, thus killing the fixed cells, it makes it possible to study molecular details that occur too rapidly or transiently to observe in living samples. Common fixatives such as formaldehyde work by disabling enzymes, coagulating, insolubilizing, and/or macromolecules, creating between them, and protecting specimens from decomposition by bacteria and fungi.
2. The process by which a single for a particular with multiple different alleles increases in in a given population such that it becomes permanently established as the only allele at that within the population's.
Any chemical compound or solution that causes the of cells, tissues, or other microscopic structures by any mechanism, thus preserving them for long-term, detailed study by methods such as embedding,, and microscopy. Common fixatives include dilute solutions of ethanol, acetic acid, formaldehyde, and osmium tetroxide, among others.
Having one or more.
A long, thin, hair-like appendage protruding from the surface of some cells, which serves locomotory functions by undulating in a way that propels the cell through its environment or by effecting the movement of and solutes past the cell surface. Many unicellular organisms, including some bacteria, protozoa, and algae, bear one or more flagella, and certain cell types in multicellular organisms, namely sperm cells, also have flagella. Eukaryotic flagella are essentially just longer versions of, often up to 150 micrometres in length, while bacterial flagella are typically smaller and completely different in structure and mechanism of action.
The prevailing scientific model of the structure and properties of, according to which the typical membrane consists of of amphipathic interspersed with a dynamic variety of embedded,, and , all of which behave as if suspended in a "two-dimensional liquid", constantly moving laterally between the lipids and interacting with each other and with the and the. The membrane as a whole thus retains a fluidity and elasticity which allow it to change shape and adapt to the cell's environment.
A type of where the probes are with a that is naturally fluorescent when exposed to light at particular wavelengths, making it possible to detect the ' locations of complementary sequences with fluorescence microscopy. FISH is commonly used to visualize the physical locations of specific genes on chromosomes.
An experimental approach in in which a researcher starts with a specific known and attempts to determine the genetic basis of that phenotype by any of a variety of laboratory techniques, commonly by random in the organism's genome and then for changes in the phenotype of interest. Observed phenotypic changes are assumed to have resulted from the mutation present in the screened sample, which can then be to specific genomic and ultimately to one or more specific. This methodology contrasts with, in which a specific gene or its gene product is individually manipulated in order to identify the gene's function.
A that changes a gene from to mutant; the initial mutation which a reverses.
A type of in a caused by the or of a number of that is not divisible by three. Because of the triplet nature by which nucleotides code for amino acids, a mutation of this sort causes a shift in the of the nucleotide sequence, resulting in the sequence of downstream of the mutation site being completely different from the original.
See '.
An organization that works with others "to develop standards for biological research data quality, annotation and exchange" as well as software tools that facilitate their use.
G
A technique used in to produce a visible by staining the condensed chromosomes with Giemsa stain. The staining produces consistent and identifiable patterns of dark and light "bands" in regions of, which allows specific chromosomes to be easily distinguished.
A cell that is the product of a progenitor and the final product of the in sexually reproducing multicellular organisms. Gametes are the means by which an organism passes its genetic information to its offspring; during fertilization, two gametes are fused into a single .
The process by which eukaryotic divide and into . Depending on the organism, gametes may be generated from haploid germ cells by or germ cells by.
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Any segment or set of segments of a molecule that contains the information necessary to produce a functional transcript in a controlled manner. In living organisms, genes are often considered the fundamental units of and are typically encoded in. A particular gene can have multiple different versions, or, and a single gene can result in a that influences many different.
See '.
The number of copies of a particular present in a. Gene dosage directly influences the amount of a cell is able to express, though a variety of controls have evolved which tightly . Changes in gene dosage caused by mutations include.
A type of defined as any of a region of that contains a. Compare '.
The set of processes by which the information encoded in a is used in the synthesis of a, such as a protein or a, or otherwise made available to influence one or more ; both the product and the gene encoding it are then said to be expressed. Canonically, the first step is, which produces a molecule complementary to the molecule in which the gene is encoded. For protein-coding genes, the second step is, in which the messenger RNA is read by a to produce a and ultimately a protein. The information contained within a DNA sequence need not necessarily be transcribed and translated to exert an influence on molecular events, however: broader definitions encompass a huge variety of other ways in which genetic information can be expressed.
A database of functional genomics and data derived from experimental assays and and managed by the National Center for Biotechnology Information.
The union, either by natural mutation or by laboratory techniques, of two or more previously independent genes that code for different gene products such that they become subject to control by the same systems. The resulting hybrid sequence is known as a.
Any of a variety of methods used to precisely identify the of a particular within a DNA molecule and/or the physical or distances between it and other genes.
A being studied in a scientific experiment, especially one that is the focus of a technique such as.
Any of the biochemical material resulting from the of a, most commonly interpreted as the functional produced by of the gene or the fully constructed produced by of the transcript, though molecules such as may also be considered gene products. A measurement of the quantity of a given gene product that is detectable in a cell or tissue is sometimes used to infer how active the corresponding gene is.
The broad range of mechanisms used by cells to control the activity of their genes, especially to allow, prohibit, increase, or decrease the production or of specific, such as or. Gene regulation increases an organism's versatility and adaptability by allowing its cells to express different gene products when required by changes in its environment. In multicellular organisms, the regulation of gene expression also drives and in the, enabling the creation of a diverse array of from the same.
Any mechanism of which drastically reduces or completely prevents the of a particular gene. Gene silencing may occur naturally during either or. Laboratory techniques often exploit natural silencing mechanisms to achieve.
The insertion of a functional or gene or part of a gene into an organism with the intention of correcting a, either by direct substitution of the defective gene or by supplementation with a second, functional version.
A technology used to simultaneously inactivate, identify, and report the of a target gene in a mammalian genome by introducing an insertional consisting of a gene and/or a flanked by an upstream site and a downstream termination sequence.
1. In any given organism, a single reproductive cycle, or the phase between two consecutive reproductive events, i.e. between an individual organism's reproduction and that of the progeny of that reproduction; or the actual or average length of time required to complete a single reproductive cycle, either for a particular or for a population or species as a whole.
2. In a given population, those individuals who are equally removed from a given by virtue of the same number of reproductive events having occurred between them and the ancestor.
A set of rules by which information encoded within is into by living cells. These rules define how sequences of triplets called specify which will be added next during. The vast majority of living organisms use the same genetic code but variant codes do exist.
Any illness, disease, or other health problem directly caused by one or more abnormalities in an organism's which are congenital and not acquired later in life. Causes may include a to one or more, or a such as an of a particular chromosome. The mutation responsible during embryonic development or may be from one or both parents, in which case the genetic disorder is also classified as a. Though the abnormality itself is present before birth, the actual disease it causes may not develop until much later in life; some genetic disorders do not necessarily guarantee eventual disease but simply of developing it.
A measure of the genetic divergence between species, populations within a species, or individuals, used especially in to express either the time elapsed since the existence of a or the degree of differentiation in the comprising the of each population or individual.
The direct, deliberate manipulation of an organism's genetic material using any of a variety of biotechnology methods, including the or of, the transfer of genes within and between species, the of existing sequences, and the construction of novel sequences using. Genetic engineering encompasses a broad set of technologies by which the genetic composition of individual cells, tissues, or entire organisms may be altered for various purposes, commonly in order to study the functions and of individual genes, to produce hormones, vaccines, and other drugs, and to create for use in research and agriculture.
A specific, easily identifiable, and usually highly or other with a known location on a that can be used to identify the individual or species possessing it.
Any reassortment or exchange of genetic material within an individual organism or between individuals of the same or different species, especially that which creates. In the broadest sense, the term encompasses a diverse class of naturally occurring mechanisms by which are copied or physically transferred into different genetic environments, including during or or as a normal part of ; events such as,, or ; or errors in or cell division. Artificial recombination is central to many techniques which produce.
The redundant encoding of two or more distinct that ultimately perform the same biochemical function. in one of these genes may have a smaller effect on fitness than might be expected, since the redundant genes often compensate for any and obviate any.
A graph that represents the regulatory complexity of. The vertices are represented by various regulatory elements and while the edges are represented by their interactions. These network structures also represent functional relationships by approximating the rate at which genes are.
A broad class of various procedures used to identify features of an individual's particular chromosomes, genes, or proteins in order to determine parentage or ancestry, diagnose vulnerabilities to heritable diseases, or detect alleles associated with increased risks of developing. Genetic testing is widely used in human medicine, agriculture, and biological research.
Any organism whose genetic material has been altered using techniques, particularly in a way that does not occur naturally by mating or by natural.
The field of biology that studies,, and in living organisms.
1. The entire complement of genetic material contained within the of an organism,, or virus.
2. The collective set of or genetic shared by every member of a population or species, regardless of the different that may be present at these loci in different individuals.
The total amount of contained within one copy of a, typically measured by mass or by the total number of . For organisms, genome size is often used interchangeably with.
A method of in which the of fragments in a are assembled into a longer sequence, such as that of a full chromosome or the entire genome, by placing fragments with overlapping ends, known as, adjacent to each other. By repeating this procedure, one can hypothetically determine the correct arrangement of contigs for the entire sequence.
The contained in, as opposed to the contained in separate structures such as or organelles such as or.
An phenomenon that causes to be in a manner dependent upon the particular parent from which the gene was inherited. It occurs when epigenetic marks such as or are established or "imprinted" in the of a parent organism and subsequently maintained through cell divisions in the of the organism's progeny; as a result, a gene in the progeny that was inherited from the father may be expressed differently than another copy of the same gene that was inherited from the mother.
A region of a that shows evidence of from another organism. The term is used especially in describing microbial genomes such as those of bacteria, where genomic islands having the same or similar sequences commonly occur in species or strains that are otherwise only distantly related, implying that they were not passed on through vertical descent from a common ancestor but through some form of lateral transfer such as. These islands often contain functional genes which confer adaptive traits such as.
An interdisciplinary field that studies the structure, function, evolution, mapping, and editing of entire, as opposed to individual.
The ability of certain chemical agents to cause damage to genetic material within a living cell, which may or may not result in a permanent. Though all are genotoxic, not all genotoxic compounds are mutagenic.
The entire complement of present in a particular individual's, which gives rise to the individual's.
The process of determining differences in the of an individual by examining the in the individual's using and comparing them to another individual's sequences or a reference sequence.
Any that gives rise to the of a sexually reproducing organism. Germ cells are the vessels for the genetic material which will ultimately be passed on to the organism's descendants and are usually distinguished from, which are entirely separate from the.
1. In multicellular organisms, the subpopulation of cells which are capable of passing on their genetic material to the organism's progeny and are therefore distinct from, which cannot pass on their genetic material except to their own immediate daughter cells. Cells of the germ line are called.
2. The of germ cells, spanning many generations, that contains the genetic material which has been passed on to an individual from its ancestors.
A unit of length equal to one billion in molecules or one billion in duplex molecules such as.
Any that can be converted into via, as opposed to the, which can be converted into ketone bodies. In humans, 18 of the 20 amino acids are glucogenic; only leucine and lysine are not. Five amino acids are both glucogenic and ketogenic.
The chain of reactions that results in the generation of from some non-carbohydrate carbon substrates, including the. It is one of two primary used by most animals to maintain blood sugar levels, especially during periods of fasting, starvation, and intense exercise.
A simple sugar with the molecular formula and the most abundant in nature, being the primary product of photosynthesis, where it is made in a sunlight-powered reaction of water with carbon dioxide. All living organisms are capable of metabolizing glucose via, an exergonic pathway which for most organisms is the primary means of obtaining chemical energy to power cellular activities. Metabolic glucose is usually stored in the form of large polymeric aggregates such as amylose in plants and in animals, and is released by the breakdown of these polymers via.
A fine, hair-like coating covering the outer surface of virtually all cells, composed of a layer of various branching and which are embedded within and protrude from the face of the. These molecules play critical roles in,, and intercellular adhesion.
A branched composed of as many as 30,000 covalently bonded units of the which functions as the primary form of short-term energy storage in most animal cells. Glycogen reserves are especially abundant in muscle and liver cells, where they can be metabolized at-need into their component glucoses as a means of buffering blood sugar levels, a process known as.
A in which polymeric molecules are broken down into individual monomers by the sequential removal of glucose units via phosphorolysis, a reaction catalyzed by the enzyme glycogen phosphorylase. Glycogenolysis is one of two primary pathways used in animal tissues to generate free glucose for the maintenance of blood sugar levels, the other being.
Any of a subclass of consisting of a central polar molecule which is covalently attached to one or more or via, as well as to one or more long, non-polar chains. Glycolipids are one of three major types of comprising all biological membranes, along with and.
The in which sugars such as are broken down into simpler molecules, releasing chemical energy which can then be used for various cellular functions. In a series of ten enzyme-catalyzed reactions, each molecule of glucose is converted into two molecules of, with the free energy liberated in this process simultaneously being used to form high-energy bonds in two molecules of reduced and two molecules of . In conditions pyruvate and NADH are further oxidized in the ; in conditions NADH itself subsequently reduces pyruvate to lactate.
A with one or more molecules, typically short chains, covalently attached to one or more of its amino acid side chains. Proteins exposed on the outer surface of the or secreted into the extracellular space are commonly modified in this way, after which they are said to be.
Any of a class of capable of breaking one or more in molecules, commonly found in.
Any chemical compound consisting of a molecule covalently bonded to another molecule containing a hydroxyl group via one or more . When all of the compound's substituents are carbohydrates, the glycoside is a.
A covalent ether bond that connects a carbon atom within a molecule or a carbohydrate derivative to another substituent or functional group, which may or may not be another carbohydrate; such bonds form as the result of a dehydration reaction between hydroxyl groups on each molecule. A substance containing a glycosidic bond is known as a.
The attachment of a carbohydrate molecule to an amino acid residue within a or by covalent bonding, a process which takes place in or near the.
See '.
See '.
A used as one of the four standard nucleobases in both and molecules. Guanine forms a with.
The proportion of in a that are either or , typically expressed as a percentage. DNA and RNA molecules with higher GC-content are generally more thermostable than those with lower GC-content due to molecular interactions that occur during base stacking.
One of the four standard used in molecules, consisting of a with its N9 nitrogen to the C1 carbon of a sugar. Guanine bonded to is known as, which is the version used in.
A short which complexes with Cas and, by annealing to a specific complementary sequence in a molecule, serves to "guide" these proteins to viral DNA introduced by foreign pathogens, which can then be digested and degraded as part of an adaptive immune defense employed by bacteria and archaea. Custom-made guide RNAs are designed by scientists to target specific genomic loci in CRISPR-Cas.
H
A characteristic that commonly forms in self-complementary by intramolecular between different parts of the same linear, molecule. The resulting conformation resembles a hairpin, where non-adjacent lengths of nucleotides form hydrogen bonds with each other, creating a local double-stranded which ends in a circle of unpaired nucleotides. Hairpin loops form readily in single-stranded DNA molecules containing and are especially common in large RNA molecules, where they play various roles in promoting or inhibiting the formation of other secondary structures, stabilizing, providing recognition sites for, or serving as for enzymes.
[Image:Stem-loop.svg|thumb|right|350px|The structure of a basic in a single-stranded RNA molecule]
Having one copy of each, with each copy not being part of a pair. Contrast ' and '.
Any of a class of -dependent that move directionally along the and catalyze the separation of the two complementary of molecules, permitting a wide variety of vital processes to take place, e.g.,, and.
In a organism, having just one at a given . Hemizygosity may be observed when only one copy of a is present in a normally diploid cell or organism, or when a segment of a chromosome containing one copy of an allele is, or when a gene is located on a in the heterogametic sex ; for example, in human males with normal chromosomes, almost all genes are said to be hemizygous because there is only one and few of the same genes exist on the.
The storage, transfer, and expression of molecular information in biological organisms, as manifested by the passing on of from parents to their, either through sexual or asexual reproduction. Offspring cells or organisms are said to inherit the genetic information of their parents.
A compact, highly condensed form of characterized chiefly by the close spatial proximity of adjacent and the consequent inaccessibility of intervening DNA sequences to, which contrasts with the more open and accessible form known as. The transcription of genes located within heterochromatic regions of chromosomes is therefore relatively limited, and so the formation of heterochromatin at specific loci is an important means of regulating. Establishment of heterochromatin is associated with the of specific residues within specific, such as of the ninth lysine residue of histone H3 ; the presence of these modifications at a specific locus signals the recruitment of other proteins which cause local DNA condensation. Many repetitive and structurally important regions of chromosomes are nearly always compacted in so-called, while the compaction of is more temporary.
See '.
A or protein composed of two different which are in the quaternary structure of a multimeric complex. Contrast '.
Any of a set of molecules of widely variable size occurring in the nucleus and united by their rapid turnover rate during. HnRNA represents all of the various transcriptional products of, including both of and, from raw, unprocessed to,, and mature and all of the intermediate forms in between.
A cell containing with different genotypes, resulting from the of two or more genetically distinct cells, either naturally or artificially.
The of a foreign or any other foreign DNA sequence within a host organism which does not naturally contain the same gene. Insertion of foreign into heterologous hosts using is a common biotechnology method for studying gene structure and function.
Describing a method or system capable of very large numbers of samples or of processing very large quantities of data extremely rapidly, generally by utilizing automation and miniaturization to greatly increase speed and efficiency. For example, high-throughput sequencing refers to modern technologies that can produce sequence reads for hundreds of millions of DNA fragments simultaneously, allowing scientists to quickly and inexpensively.
The study or analysis of the microscopic anatomy of biological or of within tissues, particularly by making use of specialized techniques to distinguish structures and functions based on visual morphology and differential staining. In practice the term is sometimes used more broadly to include.
Any of a class of highly alkaline responsible for DNA into structural units called in eukaryotic cells. Histones are the chief protein components of, where they associate into which act as "spools" around which the linear DNA molecule winds. They play a major role in and.
The complex of eight proteins around which double-stranded DNA wraps within a. The canonical histone octamer consists of two each of histones H2A, H2B, H3, and H4, which pair with each other symmetrically to form a ball-shaped cluster around which DNA winds through interactions with the histones' surface, though may replace their analogues in certain contexts.
The of proteins by the chemical attachment of various molecules or functional groups to specific amino acid residues. Because histones form the of, the modification of exposed parts of their polypeptide chains is used to regulate gene expression by marking them with that signal the recruitment of other proteins to induce conformational changes that variously widen or condense the spacing of nucleosomes along strands of DNA, thereby changing the accessibility of nearby DNA sequences to transcriptional machinery. Histones are modified by many different labels, most commonly,,,, and.
See '.
Having no single but rather multiple assembly sites dispersed along the entire length of the chromosome. During cell division, the of holocentric chromosomes move apart in parallel and do not form the classical V-shaped structures typical of chromosomes.
Any of a class of DNA approximately 180 base pairs in length occurring near the of certain eukaryotic genes and encoding a 60-amino acid domain, known as a, which is capable of via a characteristic helix-turn-helix motif. Homeobox-containing genes are translated into homeodomain-containing proteins, which commonly transcription or translation by binding to other genes or messenger RNAs containing. The products of many homeotic genes, exemplified by the, are of critical importance in developmental pathways.
Any DNA or RNA that is specifically and bound by the of a homeodomain-containing protein.
A, typically 60 in length, found near the of certain eukaryotic, characterized by a highly helix-turn-helix that binds with strong affinity to the backbone of specific in DNA or RNA molecules. A protein may have one or more homeodomains, each of which is specific to a different recognition sequence. Many homeodomain-containing proteins function as by binding to sequences within and blocking or recruiting other proteins, such as or of the. Homeodomains are the versions of, though the terms are often used interchangeably.
A or protein composed of two identical which are in the quaternary structure of a multimeric complex. Contrast '.
A set of two matching, one maternal and one paternal, which pair up with each other inside the nucleus during. They have the same at the same, but may have different.
A type of in which nucleotide sequences are exchanged between two similar or identical molecules of, especially that which occurs between. The term may refer to the recombination that occurs as a part of any of a number of distinct cellular processes, most commonly or during in eukaryotes and in prokaryotes. Contrast '.
Any process by which genetic material is transferred between unicellular and/or multicellular organisms other than by vertical transmission from parent to offspring, e.g. bacterial conjugation.
Any that is at a relatively constant level across many or all known conditions and cell types. The of housekeeping genes typically play critical roles in the maintenance of cellular integrity and basic metabolic function. It is generally assumed that their expression is unaffected by experimental or pathological conditions.
A subset of highly -containing whose protein products function as essential for the proper organization of the body plan in developing animal, ensuring that the correct structures are formed in the correct places. Hox genes are usually arranged on a chromosome in arrays and are sequentially during development, with the sequence of gene activation corresponding to their physical arrangement within the genome and/or the physical layout of the tissues in which they are expressed along the organism's anterior–posterior axis.
A collaborative international scientific research project with the goal of all of the and identifying and all of the within human cells, and ultimately of assembling a complete for the human species. The project was launched in 1990 by a consortium of federal agencies, universities, and research institutions and was declared complete in 2003. Because each individual human being has a unique genome, the finished reference genome is a of sequences obtained by sampling DNA from thousands of individuals across the world and does not represent any one individual.
See '.
The that results from combining the qualities of two organisms of different genera, species, breeds, or varieties through sexual reproduction. Hybrids may occur naturally or artificially, as during of domesticated animals and plants. Reproductive barriers typically prevent hybridization between distantly related organisms, or at least ensure that hybrid offspring are sterile, but fertile hybrids may result in speciation.
1. The process by which a organism is produced from two organisms of different genera, species, breeds, or varieties.
2. The process by which two or more molecules with nucleotide sequences with each other in solution, creating or molecules via the formation of hydrogen bonds between the complementary nucleobases of each strand. In certain laboratory contexts, especially ones in which long strands hybridize with short , hybridization is often referred to as.
3. A step in some experimental assays in which a single-stranded DNA or RNA preparation is added to an array surface and anneals to a .
A or fragment which is artificially with a radioactive or fluorescent compound or some other detectable marker and then allowed to with DNA or RNA sequences in order to detect the presence of those complements in a heterogeneous sample or their specific ' ; or an in which this procedure is performed. As with antibodies in, nucleic acid probes bind with high specificity to their target sequences, permitting visualization of the targets, if present, against a non-specific background, whether in a or or even '. A unique advantage of hybridization probes is that the of the hybridization reaction is easily modifiable by changing the temperature and salt concentration, making it possible for the same probe to bind to sequences with differing degrees of complementarity. Hybridization probes are employed in and and as part of many other laboratory methods. See also '.
Soluble in or having an affinity for water or other polar compounds; describing a polar molecule, or a moiety or functional group within a molecule, which participates in intermolecular interactions such as hydrogen bonding with other polar molecules and therefore readily dissolves in polar solvents such as water or aqueous solutions. Unlike compounds, hydrophilic compounds can form energetically favorable contacts with the aqueous phase of biological fluids and so can often be suspended directly in the or exposed to extracellular spaces. Together, the contrasting properties of hydrophilicity and hydrophobicity play major roles in determining the structural and functions of most.
Having a low solubility in or affinity for water or other polar solvents; describing a non-polar molecule, or a moiety or functional group within a molecule, which cannot form energetically favorable interactions with polar compounds and which therefore tends to "avoid" or be repulsed by such compounds, instead clustering together with other hydrophobic molecules or arranging itself in a way that minimizes its exposure to its polar surroundings. This phenomenon is not so much due to the affinity of the hydrophobic molecules for each other as it is a consequence of the strong intermolecular forces that allow polar compounds such as water molecules to bond with each other; hydrophobic species are unable to form alternative bonds of equivalent strength with the polar compounds, hence they tend to be excluded from aqueous solutions by the tendency of the polar solvent to maximize interactions with itself. Hydrophobicity is a major determinant of countless chemical interactions in biological systems, including the spatial assumed by such as and, the binding of and to proteins, and the structure and properties of lipid. Contrast '.
Describing a solution containing a high concentration of dissolved solutes relative to another solution, i.e. having positive osmotic pressure, such that solvent will tend to move by osmosis across a semipermeable membrane from the solution of lower solute concentration to the solution of higher concentration until both solutions have equal concentrations. In a cell where the intracellular is hypertonic relative to the surrounding , the solvent will flow across the into the cytosol, filling the cell with extra water and diluting its contents until both sides of the membrane are. Cells placed in severely hypotonic environments may be at risk of bursting due to the sudden inflow.
A mutant that permits a subnormal expression of the gene's normal phenotype, e.g. by encoding an unstable enzyme which degrades too quickly to fully serve its function but which nevertheless is functional in some limited capacity, being generated in quantities sufficient for its reaction to proceed slowly or at low levels.
Describing a solution containing a low concentration of dissolved solutes relative to another solution, i.e. having negative osmotic pressure, such that solvent will tend to move by osmosis across a semipermeable membrane from the solution of lower solute concentration to the solution of higher concentration until both solutions have equal concentrations. In a cell where the intracellular is hypotonic relative to the surrounding , the solvent will flow across the out of the cytosol, causing the cell to lose water until both sides of the membrane are. Cells placed in severely hypertonic environments may be at risk of shriveling and desiccating due to the sudden outflow.
A naturally occurring, non-canonical that is used in some molecules and pairs with standard nucleobases in a phenomenon known as. Its form is known as, which is the reason it is commonly abbreviated with the letter in sequence reads.
I
See '.
A diagrammatic or schematic of the entire set of within a cell or genome, in which annotated illustrations depict each chromosome in its most idealized form so as to facilitate the easy identification of sequences, structural features, and physical distances, which may be less apparent in photomicrographs of the actual chromosomes.
See '.
The natural or artificial changing of a with a normally finite lifespan into one with a hypothetically infinite lifespan, capable of dividing indefinitely without as long as essential nutrients are available and conditions are conducive for. Cells that undergo such a change are said to be immortalized. Mutations that cause immortalization occur naturally in the that cause cancer but can also be induced artificially, which makes it possible to certain cell lines ' for prolonged periods. Immortalized cell lines are thus broadly useful for experimental purposes and in many biotechnology applications. Immortalized eukaryotic cells are commonly obtained by isolating them from a naturally occurring neoplasm, or may be generated from normal cells by introducing viral genes, by artificially proteins required for immortality such as, or by normal cells with cancer cells. Though are also capable of continuous self-renewal and are thus technically 'immortal', their immortalization is not abnormal because they are an ordinary part of the development of multicellular organisms.
A family of laboratory techniques in which a particular or is conjugated to a fluorescent dye and then allowed to bind specifically to its complementary antibody or antigen, if any exists, in a, tissue section or smear,, membrane, or any other context. The presence or absence of the complement and its specific location can be visualized by illuminating the sample with ultraviolet light and observing the fluorescence from the conjugated fluorophore, often under a microscope.
Capable of provoking or inducing an immune response, as with an or a vaccine.
A branch of which makes use of to some kind of in order to detect the presence or of complementary antigenic structures in tissue samples. See also '.
The use of an to a or to bind a specific within a target substance and thereby make the substance visible amidst a background of non-specific substances, allowing for detection of the target in a biological sample. The term originally referred to antibody-based staining of tissue sections with strong dyes or colorants, known as, but in modern usage encompasses a much broader range of laboratory methods united by their use of antibodies to specific biomolecules with visually conspicuous compounds.
Conducted, produced, or analyzed by means of computer modeling or simulation, as opposed to a real-world trial.
Occurring or made to occur in a natural, uncontrolled setting, or in the natural or original position or place, as opposed to in a foreign cell or tissue type or.
A assay in which a, single-stranded DNA or RNA molecule or containing a sequence that is to a particular DNA or RNA sequence is allowed to with its complement ', i.e. in its natural context, such as within cells or tissue sections, in order to of the complementary sequence within this context. The label may be a radioactive compound,, or, permitting detection by a variety of visualization techniques. In situ hybridization is commonly used to identify the physical locations of specific DNA sequences such as genes and regulatory elements on, which can provide insight into chromosomal structure and integrity; to determine the subcellular locations where various types of RNA accumulate and interact with other molecules; and to visualize the tissues and organs within an organism where specific genes are at various developmental stages.
Occurring or made to occur in a laboratory vessel or other controlled artificial environment, e.g. in a test tube or a petri dish, as opposed to or.
Occurring or made to occur inside the cells or tissues of a living organism; or, in the broadest sense, in any natural, unmanipulated setting. Contrast ' and '.
A term referring to either an or a of one or more in a nucleic acid sequence.
A protein that binds to a or to an .
A whose is either responsive to environmental change or dependent on its host cell's position within the cell cycle.
1. Read or transcribed in the same as another gene or sequence; not requiring a shift in reading frame to be intelligible or to result in a functional.
2. Not causing a.
See '.
See '.
Any of various which bind to the or of during the initiation of and thereby play roles in regulating when and how protein synthesis occurs. Initiation factors are essential for assembly of the initiation complex and for to properly associate with the ribosome and the. They are frequent targets of and which can respectively increase or decrease the rate of translation. Though their functions are largely conserved, they are distinguished by the taxonomic domain in which they occur: bacterial initiation factors, archaeal initiation factors, and eukaryotic initiation factors.
A naturally occurring, non-canonical consisting of a with its N9 nitrogen to the C1 carbon of a sugar. Inosine may be incorporated into certain molecules such as the of some, and occurs as an intermediate in the breakdown of to uric acid and in the recycling of adenosine by.
A type of in which one or more are added to a. Contrast '.
Any nucleotide sequence that is naturally or artificially into another sequence. The term is used in particular to refer to the part of a that codes for those proteins directly involved in the transposition process, e.g. the enzyme. The coding region in a transposable insertion sequence is usually flanked by short, and the structure of larger transposable elements may include a pair of flanking insertion sequences which are themselves inverted.
The alteration of a DNA sequence by the of one or more nucleotides into the sequence, either naturally or artificially. Depending on the precise location of the insertion within the target sequence, insertions may partially or totally inactivate or even upregulate a or biochemical pathway, or they may be, leading to no substantive changes at all. Many techniques rely on the insertion of exogenous genetic material into host cells in order to study gene function and expression.
A specific DNA sequence that prevents a gene from being influenced by the or of nearby genes.
Any of a class of which are permanently embedded within or attached to the . Integral membrane proteins can be subclassified into, which span the entirety of the membrane, and, which adhere only to one side.
Any of a class of which are permanently attached to one side of the by any means but which do not completely span the membrane. Contrast '.
Any of a class of which span the entirety of the, extending from the interior or side of the membrane to the exterior or side. Transmembrane proteins typically have hydrophilic exposed to each side as well as one or more hydrophobic domains crossing the nonpolar space inside the, by which they are further classified as single-pass or multipass membrane proteins. As such many transmembrane proteins function as or to permit or prohibit the movement of specific molecules or ions across the membrane, often undergoing conformational changes in the process, or as in pathways. Contrast '.
A consisting of a containing the gene for a, -specific recognition sites, and a that governs the expression of one or more genes conferring adaptive traits on the host cell. Integrons usually exist in the form of circular DNA fragments, through which they facilitate the rapid adaptation of bacteria by enabling of antibiotic resistance genes between different bacterial species.
Any sequence of one or more within a precursor that is excised by during and is therefore absent from the mature protein, analogous to the spliced out of RNA transcripts. Contrast '.
Any chemical compound that disrupts the alignment and in the complementary strands of a molecule by.
The insertion, naturally or artificially, of chemical compounds between the planar of a molecule, which generally disrupts the hydrogen bonding necessary for.
Between two or more. Contrast '; see also '.
Any DNA sequence that is located between the of one and the of the following gene in a transcription unit. See also '.
A in which both the male and female parents are at a particular.
Any sequence of that is located between functional.
See '.
The abbreviated pause in activities related to cell division that occurs during in some species, between the first and second meiotic divisions. No occurs during interkinesis, unlike during the normal that precedes meiosis I and.
A sequence present in some that permits recognition by the and thus the initiation of even in the absence of a, which in eukaryotes is otherwise required for assembly of the initiation complex. IRES elements are often located in the, but may also be found in other positions.
An international non-governmental organization devoted to promoting scientific research and education in the disciplines of and, primarily by standardizing biochemical nomenclature, developing and publishing laboratory methods, and awarding grants and fellowships to students and researchers.
All stages of the excluding. A typical cell spends most of its life in interphase, during which it conducts everyday as well as the complete of its genome in preparation for or.
Within a or cells; i.e. inside the. Contrast ' and '.
See '.
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A that lacks any distinct, fixed three-dimensional structure or organization under physiological conditions, instead changing continuously and randomly between multiple transient rather than folding into any one stable conformation, especially in the absence of specific macromolecular interaction partners. The majority of eukaryotic proteins contain domains with intrinsic structure alongside unstructured domains. lacking intrinsic order are generally characterized by high proportions of charged and hydrophilic amino acids and low proportions of hydrophobic amino acids, making them inherently flexible, accessible, and modifiable, which allows the same peptide sequence to have distinct functions across a wide variety of biochemical circumstances. They are frequently enriched in and are common targets of, giving them important roles in pathways and as hubs in.
Any within a functional that is removed by during of the and is therefore absent from the final mature mRNA. The term refers to both the sequence as it exists within a DNA molecule and to the corresponding sequence in RNA transcripts. Contrast '.
See '.
A whose DNA sequence is nested within an of another gene and hence surrounded by non-coding intronic sequences.
The infolding of a toward the interior of a cell or organelle, or of a sheet of cells toward the interior of a developing,, or organ, forming a distinct membrane-lined pocket. In the case of individual cells, the invaginated pocket may proceed to separate from the source membrane entirely, creating a membrane-bound within the cell, as in.
A followed on the same by its own. The initial sequence and the reverse complement may be separated by any number of nucleotides, or may be immediately adjacent to each other; in the latter case, the composite sequence is also called a. Inverted repeats are by definition, a property which involves them in many biological functions and dysfunctions. Contrast '.
A type of complex which forms an spanning the of a membrane, through which specific inorganic, electrically charged ions can diffuse down their electrochemical gradients.
Any chemical compound or macromolecule that facilitates the movement of ions across biological membranes, or more specifically, any chemical species that reversibly binds electrically charged atoms or molecules. Many ionophores are lipid-soluble that catalyze the transport of monovalent and divalent cations across the hydrophobic surrounding cells and vesicles.
A large region of with a relatively homogeneous composition of, distinguished from other regions by the proportion of pairs that are - or -. The genomes of most plants and vertebrates are composed of different classes of GC-rich and AT-rich isochores.
A type of abnormal in which the arms of the chromosome are mirror images of each other. Isochromosome formation is equivalent to simultaneous and events such that two copies of either the or the comprise the resulting chromosome.
The pH at which a particular molecule, often a, carries no net electrical charge, i.e. at which it is electrically neutral in the statistical mean. The concentration of protons in the surrounding environment affects how readily molecules gain or lose protons and thus their electrical properties. When the environmental pH is greater than the molecule's pI, the molecule is negatively charged, and when the pH is less than the pI, it is positively charged. Isoelectric point is therefore important for determining the behavior of molecules exposed to electric fields, as in and ion chromatography. Proteins are least soluble at their isoelectric points because electrically neutral species do not repulse each other with electrostatic forces, such that they tend to aggregate and precipitate out of solution.
Any of a class of which catalyze the conversion of a molecule from one isomer to another, such that the product of the reaction has the same molecular formula as the original substrate but differs in the connectivity or spatial arrangement of its atoms.
Two or more that are equivalent and redundant in the sense that, despite coding for distinct, they each result in the same when set within the same. If several isomeric genes are present in a single they may be either cumulative or non-cumulative in their contributions to the phenotype.
Describing a solution containing the same concentration of dissolved solutes as another solution, such that the two solutions have equal osmotic pressure. Isotonic solutions separated from each other by a semipermeable membrane have no and thus will not exchange solvent by osmosis. Contrast ' and '.
J
See .
Any DNA sequence that appears to have no known biological function, or which acts in a way that has no positive or a net negative effect on the fitness of the in which it is located. The term was once more broadly used to refer to all, though much of this was later discovered to have a function; in modern usage it typically refers to broken or vestigial sequences and, including,,, and fragments of and retroviruses, which together constitute a large proportion of the genomes of most eukaryotes. Despite not contributing productively to the host organism, these sequences are able to persist indefinitely inside genomes because the disadvantages of continuing to copy them are too small to be acted upon by.
Any RNA-encoded sequence, especially a, that appears to have no known biological function, or whose function has no positive or a net negative effect on the fitness of the genome from which it is transcribed. Despite remaining, many still serve important functions, whereas junk RNAs are truly useless: often they are the product of accidental transcription of a sequence, or they may result from of, as with . Junk RNA is usually quickly degraded by and other cytoplasmic enzymes.
K
A which depicts the entire set of in a cell or organism by using photomicrographs of the actual chromosomes as they appear ', as opposed to the idealized illustrations of chromosomes used in. The photomicrographs are often still arranged in pairs and by size for easier identification of particular chromosomes, whereas in the actual nucleus there is seldom any apparent organization.
See '.
See '.
See '.
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The fragmentation and degeneration of the of a dying cell, during which the is destroyed and the contents of the nucleus, including, are dispersed throughout the and degraded by enzymes. Karyorrhexis is usually preceded by and may occur as a result of,, or.
A dense, organized bundle of which forms in the oocyte nucleus during oogenesis in some female eukaryotes.
The number and appearance of within the of a eukaryotic cell, especially as depicted in an organized or . The term is also used to refer to the complete set of chromosomes in a species or individual organism or to any test that detects this complement or measures the chromosome number.
The production of via the of or, an exergonic process which is used to supply energy to certain tissues during periods of carbohydrate and protein insufficiency.
Any that can be converted directly into, which can then be oxidized for energy or used as a precursor for many. This is in contrast to the, which can be converted into. In humans, seven of the 20 amino acids are ketogenic, though only leucine and lysine are exclusively ketogenic; the other five are both ketogenic and glucogenic.
The of, which releases energy that can be used to synthesize.
A unit of length equal to one thousand in molecules or one thousand in duplex molecules such as.
Any of a class of which catalyze the transfer of groups from high-energy, phosphate-donating molecules such as to one or more specific, a process known as. The opposite process, known as, is catalyzed by enzymes.
A non-specific, non-directional movement or change in activity by a cell or a population of cells in response to a stimulus, such that the rate of the movement or activity is dependent on the intensity of the stimulus but not on the direction from which the stimulus occurs. Kinesis refers particularly to cellular locomotion without directional bias, in contrast to and.
A disc-shaped which assembles around the of a during of and, where it functions as the attachment point for of the.
In, an enlarged, heavily staining that can be used as a visual marker, allowing specific chromosomes to be easily identified in the nucleus.
A method by which the normal rate of of one or more of an organism's is reduced or suppressed, either through direct modification of a DNA sequence or through treatment with a reagent such as a short DNA or RNA with a sequence to either an transcript or a gene.
A method in which one or more novel are into an organism's genome, particularly when targeted to a specific, or in which one or more existing genes are replaced by or with novel genes. This is in contrast to a, in which a gene is deleted or completely inactivated.
A method in which one or more specific are inactivated or entirely an organism's genome, by any of a variety of mechanisms which disrupt their at some point in the pathway that produces their, such that no functional gene products are produced. This allows researchers to study the function of a gene ', by observing how the organism's changes when deprived of the gene's normal effects. A complete knockout permanently inactivates the gene; a conditional knockout allows the gene to be turned on or off at will, e.g. at specific times or in specific tissues, by linking the expression of the gene to some easily modifiable biochemical state or condition. In a heterozygous knockout, only one of a diploid organism's two alleles is knocked out; in a homozygous knockout, both copies are knocked out. Contrast '.
A highly which functions as the recognition site for the initiation of in most eukaryotic, generally a sequence of 10 bases immediately surrounding and inclusive of the :. As the scans the transcript, recognition of this sequence causes the complex to commit to full assembly and the start of translation. The Kozak sequence is distinct from other recognition sequences relevant to translation such as and.
See .
L
The chemical attachment of a highly selective substance, known as a label, tag, or ', to a particular cell, protein, amino acid, or other molecule of interest, either naturally or artificially, ' or '. Natural labelling is a primary mechanism by which biomolecules specifically identify and interact with other biomolecules; important examples include,,, and. Labelling is also a common laboratory technique, where the label is typically a reactive derivative of a naturally fluorescent compound, dye, enzyme,, radioactive molecule, or any other substance that makes its target distinguishable in some way. The labelled targets are thereby rendered distinct from their unlabelled surroundings, allowing them to be detected, identified, quantified, or isolated for further study.
In, the nascent for which 's direction of synthesis is away from the, which necessitates a complex and discontinuous process in contrast to the streamlined, continuous synthesis of the other nascent strand, known as the, which occurs simultaneously. Because DNA polymerase works only in the to direction, but the lagging strand's overall direction of chain elongation must ultimately be the opposite, elongation must occur by an indirect mechanism in which a enzyme synthesizes short complementary to the template DNA, and DNA polymerase then extends the primed segments into short chains of nucleotides known as. The RNA primers are then removed and replaced with DNA, and the Okazaki fragments are joined by.
1. Any thin layer, membrane, or plate of tissue, occurring in a wide variety of structures of various scales and with various functions; e.g. a lamella made of a sheet of lipids forms a component of the between the cells of some tissues.
2. The leading edge of a motile cell, of which the lamellipodia is the most forward portion.
A transcriptionally active, highly de-condensed morphology assumed by certain during the of in the of in female insects, amphibians, birds, and some other animals. Lampbrush chromosomes are conspicuous under the microscope because the , still attached at, are gigantically elongated into large loops of unpackaged extending laterally from a series of. Large numbers of and are transcribed from the lateral loops, generating a rich pool of to be used in the immature oocyte and after fertilization, with functions in both and. Because they allow individual to be directly visualized, lampbrush chromosomes are useful models for studying chromosome organization and genome structure and for constructing high-resolution chromosome maps.
See '.
See '.
In, the nascent for which both the direction of synthesis by and the direction of overall chain elongation are toward the ; i.e. both occur in the to direction, resulting in a single, continuous elongation process with few or no interruptions. By contrast, the other nascent strand, known as the, is assembled in a discontinuous process involving the ligation of short synthesized in the opposite direction, away from the replication fork.
The boundary between the left end of an and the right end of an adjacent in a.
In, the first of five substages of, following and preceding. During leptonema, the replicated chromosomes condense from diffuse into long, thin strands that are much more visible within the.
Any that results in the premature death of the organism carrying it. lethal mutations are fatal only to, whereas lethals are fatal even in.
A common structural in and some other types of proteins, approximately 35 amino acids in length, characterized chiefly by the recurrence of the amino acid leucine every seven residues. When modeled in an idealized conformation, the leucine residues are positioned in such a way that they can interdigitate with the same or similar motifs in an alpha helix belonging to another similar polypeptide, facilitating and the formation of a complex resembling a zipper.
In biochemistry, any molecule that binds to or interacts with a on a or other, usually reversibly via intermolecular forces; or any substance that forms a complex with a biomolecule as part of a biological process. The binding of specific ligands to DNA or proteins is important in many ; for example, protein–ligand binding may result in the protein undergoing a which alters its function or affinity for other molecules.
A class of which catalyze the synthesis of large molecules such as by forming one or more chemical bonds between them, typically,,, or bonds via condensation reactions. An example is, which catalyzes the formation of between adjacent on the same strand of a DNA molecule, a reaction known as.
The joining of consecutive in the same of a molecule via the formation of a between the of one nucleotide and the of an adjacent nucleotide, a condensation reaction catalyzed by enzymes known as. This reaction occurs in fundamentally the same way in all varieties of and anabolism, natural or artificial, whether the addition of individual nucleotides to a growing strand, or the of and in previously intact molecules, or the joining of separate nucleic acid fragments into a single molecule. Ligation is the opposite of the catabolic reaction wherein phosphodiester bonds are cleaved by. It also should not be confused with the non-covalent that can occur between complementary strands; ligation refers specifically to the synthesis of the of a single strand.
The tendency of DNA sequences which are physically near to each other on the same chromosome to be together during. Because the physical distance between them is relatively small, the chance that any two nearby parts of a DNA sequence will be separated on to different during is statistically very low; such loci are then said to be more linked than loci that are farther apart. Loci that exist on entirely different chromosomes are said to be perfectly unlinked. The standard unit for measuring genetic linkage is the .
1. A short, synthetic DNA duplex containing the for a particular. In, linkers are often deliberately included in molecules in order to make them easily modifiable by permitting cleavage and of foreign sequences at precise locations. A segment of an engineered containing many such restriction sites is sometimes called a.
2. A section of chromosomal DNA connecting adjacent by binding to H1.
The number of times that the two strands of a circular molecule cross each other, equivalent to the plus the . The linking number of a closed molecule cannot be changed without breaking and rejoining the strands. DNA molecules which are identical except for their linking numbers are known as topological isomers.
Any of a heterogeneous class of organic compounds, including , waxes, sterols, and some vitamins, united only by their amphipathic or nature and consequently their very low solubility in water. Some lipids such as tend to form lamellar structures or micelles in aqueous environments, where they serve as the primary constituents of biological. Others such as can be for energy, have important functions in energy storage, or serve as molecules. Colloquially, the term "lipids" is sometimes used as a synonym for fats, though fats are more correctly considered a subclass of lipids.
A lamellar structure composed of numerous amphipathic molecules packed together in two back-to-back sheets or layers, with their "tails" directed inward and their "heads" exposed on the outer surface. This is the basic structural motif for all biological, including the surrounding all cells as well as the membranes surrounding and. Though bilayers are sometimes colloquially described as phospholipid bilayers, are just one of several classes of which form bilayers; most membranes are actually a of phospholipids,, and, interspersed and studded with various other molecules such as.
The by which are broken down via hydrolysis into a glycerol molecule and free chains. This primarily takes place in to mobilize stored energy when demand is high or supply is low.
See '.
Any water-soluble to which one or more lipid molecules are attached by covalent bonding to amino acid residues. Many classes of lipids can be conjugated to proteins, including,, and. Compare '.
1. Any small, natural globule, such as a micelle, occurring naturally in the cytoplasm; they are commonly formed by budding off from larger membrane-bound vesicles.
2. A small, spherical, artificial having at least one continuous of lipid molecules enclosing some of the medium in which it is suspended. Liposomes can be created in the laboratory by disrupting existing biological membranes and allowing complex lipids to form bilayer-bound vesicles in aqueous solution, usually with the aid of. They are used experimentally as models of natural membranes and also therapeutically for the encapsulation and delivery of pharmaceutical compounds, enzymes, nutrients, nucleic acids, lipid-based nanoparticles, and many other agents between or inside of cells.
See '.
A specific, fixed position on a where a particular or resides.
In condensed where the positioning of the creates two segments or "arms" of unequal length, the longer of the two arms of a. Contrast '.
Any of a large family of non- which together comprises one of the most widespread in eukaryotic genomes. Each LINE is on average about 7,000 base pairs in length.
A class of consisting of all of more than 200 in length that are not. This limit distinguishes lncRNA from the numerous smaller non-coding RNAs such as. See also '.
See .
The disruption and decomposition of the surrounding a cell, or more generally of any membrane-bound or, especially by,, or other chemical or mechanical processes which compromise the membrane's integrity and thereby cause the unobstructed interchange of the contents of and spaces. Lysis generally implies the complete and irreversible loss of intracellular organization as a result of the release of the cell's internal components and the dilution of the, and therefore the death of the cell. Such a cell is said to be lysed, and a fluid containing the contents of lysed cells is called a lysate. Lysis may occur both naturally and artificially, and is a normal part of the cellular life cycle.