Glossary of cellular and molecular biology (M–Z)
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 molecular genetics, biochemistry, and microbiology. It is split across two articles:
- Glossary of cellular and molecular biology lists terms beginning with numbers and those beginning with the letters A through L.
- Glossary of cellular and molecular biology lists terms beginning with the letters M through Z.
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.M
See '.
Any very large molecule composed of dozens, hundreds, or thousands of covalently bonded atoms, especially one with biological significance. Many important, such as and, are consisting of a repeated series of smaller ; others such as and may not be polymeric but are nevertheless large and complex molecules.
The larger of the two types of which occur in pairs in the cells of some ciliated protozoa. Macronuclei are highly and responsible for directing vegetative reproduction, in contrast to the , which have important functions during.
Any of a class of relatively long-lived of the mammalian immune system which are activated in response to the presence of foreign materials in certain tissues and subsequently play important roles in antigen presentation, stimulating other types of immune cells, and killing or parasitic microorganisms, diseased cells, or tumor cells.
See '.
The branch of medicine and medical science that involves the study, diagnosis, and management of, and more broadly the application of knowledge about human to medical care.
A unit of length equal to one million in molecules or one million in duplex molecules such as.
A specialized type of that occurs exclusively in sexually reproducing eukaryotes, during which is followed by two consecutive rounds of division to ultimately produce four genetically unique daughter cells, each with half the number of as the original parent cell. Meiosis only occurs in cells of the sex organs, and serves the purpose of generating haploid such as sperm, eggs, or spores, which are later fused during fertilization. The two meiotic divisions, known as Meiosis I and Meiosis II, may also include various events between.
See '.
The of a into two, especially in the context of the.
A supramolecular aggregate of amphipathic molecules which when suspended in a polar solvent tend to arrange themselves into structures which minimize the exposure of their tails by sheltering them within a ball created by their own heads. Certain types of lipids, specifically and other, commonly occur as sheets of molecules when immersed in an aqueous environment, which can themselves assume approximately spherical shapes, acting as semipermeable barriers surrounding a water-filled interior space. This is the basic structure of the biological membranes enclosing all,, and.
Any that is closely associated either or with the surrounding a,, or.
An or enclosed by its own dedicated lipid, separating its interior from the rest of the.
Any of a class of molecules which function as molecular messengers, carrying sequence information encoded in the genome to the where protein synthesis occurs. The primary products of, mRNAs are synthesized by, which builds a chain of that complement the of a ; in this way, the DNA sequence of a protein-coding is effectively preserved in the, which is subsequently processed into a mature mRNA by a series of.
A stepwise series of biochemical reactions occurring within a cell, often but not necessarily by specific, that fulfills some activity or process related to. The reactions are linked by the sharing of reactants, products, or intermediate compounds in consecutive steps, such that the product of one reaction is used as a reactant in a subsequent reaction. Byproducts are often removed from the cell as. The overall pathway may be,, or in nature. In any actively metabolizing cell, an elaborate network of interconnected metabolic pathways is required to maintain, with degradative catabolic processes providing the energy necessary to conduct anabolic biosynthesis; for example,, the, and provide the used in fatty acid synthesis. The flux of through each pathway is regulated by the needs of the cell and the availability of.
The complete set of chemical reactions which sustain and account for the basic processes of life in all living cells, especially those involving: 1) the conversion of energy from food into energy available for cellular activities; 2) the breakdown of food into simpler compounds which can then be used as to build complex such as,, and ; and 3) the degradation and excretion of toxins, byproducts, and other unusable compounds known as. In a broader sense the term may include all chemical reactions occurring in living organisms, even those which are not strictly necessary for life but instead serve accessory functions. Many specific cellular activities are accomplished by in which one chemical is ultimately transformed through a stepwise series of reactions into another chemical, with each reaction by a specific. Most metabolic reactions can be subclassified as or.
An intermediate or end product of, especially degradative metabolism ; or any substance produced by or taking part in a metabolic reaction. Metabolites include a huge variety of small molecules generated by cells from various and having various functions, including as inputs to other pathways and reactions, as molecules, and as stimulators, inhibitors, and of. Metabolites may result from the degradation and elimination of naturally occurring compounds as well as of synthetic compounds such as pharmaceuticals.
The complete set of chemical compounds within a cell, organelle, or any other biological sample, including both molecules and molecules.
Having a positioned in the middle of the chromosome, resulting in arms of approximately equal length.
The stage of and that occurs after and before, during which the of the replicated chromosomes align along the equator of the cell, with each attached to the.
The covalent attachment of a methyl group to a chemical compound, protein, or other biomolecule, either spontaneously or by catalysis. Methylation is one of the most widespread natural mechanisms by which and are. The in a DNA molecule inhibits recognition of the methylated sequence by, which can effectively the expression of genes. Specific within are also commonly methylated, which can change positioning and similarly or nearby loci. The opposite reaction is.
Any of a class of which catalyze the covalent bonding of a methyl group to another compound, protein, or biomolecule, a process known as.
A group that "aims to provide a standard for the representation of data that would facilitate the exchange of microarray information between different data systems".
Any of a diverse class of small or found in the cells of many eukaryotes, especially plants and animals, usually having some specific metabolic function and occurring in great numbers in certain specialized cell types.,,, and are often considered microbodies.
A type of very small, generally less than 20,000 in size, present in the of some organisms.
A that is too short to cause any apparent change in morphology under a light microscope, though it may still be detectable with other methods such as.
A long, thin, flexible, rod-like structure composed of polymeric strands of proteins, usually actins, that occurs in abundance in the of eukaryotic cells, forming part of the. Microfilaments comprise the cell's structural framework. They are modified by and interact with numerous other cytoplasmic proteins, playing important roles in cell stability, motility, contractility, and facilitating changes in cell shape, as well as in.
The smaller of the two types of that occur in pairs in the cells of some ciliated protozoa. Whereas the larger is, the micronucleus is and generally transcriptionally inactive except for the purpose of sexual reproduction, where it has important functions during.
A type of small,, molecule that functions in of, particularly RNA, by base-pairing with complementary sequences in, which typically results in the cleavage or destabilization of the transcript or inhibits its by ribosomes.
A type of consisting of a relatively short of, in which certain are repeated, typically 5–50 times. Microsatellites are widespread throughout most organisms' genomes and tend to have higher mutation rates than other regions. They are classified as DNA, along with longer.
A small intracellular derived from fragments of observed in cells which have been homogenized.
See '.
An instrument used to cut extremely thin slices of material, known as microsections or simply sections, preparatory to observation under a microscope. Sections of tissues and cells are usually 50 nanometres to 100 micrometres in width. The process of cutting them is known as microtomy.
A fine protein filament of the cytoskeleton. Multiple filaments form the microtrabecular network.
Any of the long, generally straight, hollow tubes, about 24 nanometers in diameter and composed of interwoven polymeric filaments of the protein tubulin, found in the cytoplasm of many eukaryotic cells, where they are involved in maintaining the cell's shape and structural integrity as well as in force generation for cellular or locomotion. They also comprise the critical to and. Microtubules are rigid but transient all-purpose structural members which can be rapidly assembled and disassembled at the cell's needs. Many different microtubule-associated proteins interact with them. See also '.
A region near the center of a eukaryotic cell typically consisting of two oriented at right angles to each other and surrounded by a of associated proteins, which functions as the site of initiation for the assembly of.
A type of released when an evagination of the "buds off" into the extracellular space. Microvesicles vary in size from 30–1,000 nanometres in diameter and are thought to play roles in many physiological processes, including by shuttling molecules such as RNA and proteins between cells.
A small, slender, tubular cytoplasmic projection, generally 0.2–4 micrometres long and 0.1 micrometres in diameter, protruding from the surface of some animal cells and supported by a central core of. When present in large numbers, such as on cells lining the respiratory and alimentary tracts, they form a dense brush border which presumably serves to increase each cell's absorptive surface area.
The centrally constricted region that forms across the central axis of a cell during, constricted by the closing of the until the are finally separated, but occasionally persisting as a tether between the two cells for as long as a complete.
In plant cells, the outermost layer of the ; a continuous, unified layer of extracellular pectins which is the first layer deposited by the cell during and which serves to cement together the primary cell walls of adjacent cells.
A commercial standard developed by for the storage and sharing of data.
A commercial standard developed by and based on in order to facilitate the storage and sharing of data.
A region of, in which certain DNA are . In the human genome, minisatellites occur at more than 1,000 loci, especially in and, and exhibit high mutation rates and high variability between individuals. Like the shorter, they are classified as and are a type of.
See '.
See '.
An incorrect of on of or ; i.e. the presence in one strand of a duplex molecule of a base that is not complementary to the base occupying the corresponding position in the other strand, which prevents normal hydrogen bonding between the bases. For example, a paired with a would be a mismatch, as guanine normally pairs with.
A type of which results in a that codes for a different than in the unmutated sequence. Compare '.
The insertion of an incorrect in a growing chain during, i.e. the inclusion of any amino acid that is not the one specified by a particular in an transcript. Mistranslation may originate from a or from a malfunctioning.
The set of DNA molecules contained within, usually one or more circular representing a semi-autonomous which is physically separate from and functionally independent of the in the cell's nucleus. The mitochondrial genome encodes many unique enzymes found only in mitochondria.
A highly pleiomorphic found in the of nearly all eukaryotic cells, usually in large numbers in the form of sausage-shaped structures 5–10 micrometres in length, enclosed by a double membrane, with the inner membrane infolded in an elaborate series of so as to maximize surface area. Mitochondria are the primary sites of synthesis, where ATP is regenerated from via, as well as many supporting pathways, including the and the. Like other, mitochondria contain encoded in molecules which replicate independently of the, as well as their own unique set of,,,, and with which to direct transcription and translation of their genes. The majority of the found in mitochondria are encoded by nuclear genes, however, such that mitochondria are only partially autonomous. These observations suggest mitochondria evolved from symbiotic living inside eukaryotic cells.
Any substance or stimulus that promotes or induces, or more generally which causes cells to re-enter the.
The selective degradation of by means of ; i.e. the mitochondrion initiates its own degradation. Mitophagy is a regular process in healthy populations of cells by which defective or damaged mitochondria are recycled, preventing their accumulation. It may also occur in response to the changing needs of the cell, e.g. during certain developmental stages.
In cells, the part of the during which the of the takes place and replicated are separated into two distinct nuclei. Mitosis is generally preceded by the of, when the cell's, and either occurs simultaneously with or is followed by, when the and are divided into two new. Colloquially, the term "mitosis" is often used to refer to the entire process of cell division, not just the division of the nucleus.
The proportion of cells within a sample which are undergoing at the time of observation, typically expressed as a percentage or as a value between 0 and 1. The number of cells dividing by mitosis at any given time can vary widely depending on organism,, developmental stage, and media, among other factors.
The abnormal between during . during mitosis is relatively uncommon; in the laboratory, it can be induced by exposing dividing cells to high-energy electromagnetic radiation such as X rays. As in meiosis, it can separate alleles and thereby propagate potentially significant changes in zygosity to, though unless it occurs very early in development this often has little or no phenotypic effect, since any phenotypic variance shown by mutant lineages arising in terminally differentiated cells is generally masked or compensated for by neighboring cells.
The process by which most animal cells undergo an overall change in shape during or preceding, abandoning the various complex or elongated shapes characteristic of and rapidly contracting into a rounded or spherical morphology that is more conducive to. This phenomenon has been observed both ' and '.
See '.
The presence of more than one different level, i.e. more than one number of sets of, in different cells of the same cellular population.
Any genetic material that can move between different parts of a or be transferred from one species or to another within a single. The many types of MGEs include, bacterial, bacteriophage elements which integrate into host genomes by viral, and.
The complete set of within a particular, cell, species, or other taxon, including all,,, and other self-splicing nucleic acid molecules.
The branch of biology that studies biological activity at the molecular level, in particular the various mechanisms underlying the biological processes that occur in and between, including the structures, properties, synthesis, and modification of such as and, their interactions with the chemical environment and with other biomolecules, and how these interactions explain the observations of classical biology. Molecular biology relies largely on laboratory techniques of physics and chemistry to manipulate and measure microscopic phenomena. It is closely related to and overlaps with the fields of,, and.
Any of various methods designed to a particular molecule, usually a or a, many times inside the cells of a natural host. Commonly, a fragment containing a is into a , which bacterial cells are then induced to uptake in a process known as. The bacteria, carrying the recombinant plasmid, are then allowed to proliferate naturally in, so that each time the bacterial cells divide, the plasmids are replicated along with the rest of the bacterial genome. Any functioning gene of interest within the plasmid will be by the bacterial cells, and thereby its will also be cloned. The plasmids or gene products, which now exist in many copies, may then be extracted from the bacteria and purified. Molecular cloning is a fundamental tool of employed for a wide variety of purposes, often to study, to amplify a specific gene product, or to generate a.
A branch of that employs methods and techniques of to study the structure and function of and at the molecular level. Contrast '.
A set of as it exists inside the of an immature such as an ootid or spermatid, i.e. a cell which is a product of but is not yet a mature gamete.
Having only one. Contrast ' and '.
Describing cells, proteins, or molecules descended or derived from a single or made in response to a single unique compound. Monoclonal are raised against only one or can only recognize one unique on the same antigen. Similarly, the cells of some and may be described as monoclonal if they are all the asexual progeny of one original. Contrast '.
A type of large of the mononuclear phagocyte system in mammals, characterized by pale-staining cytoplasm and a kidney-shaped or horseshoe-shaped nucleus. Monocytes are derived from in bone marrow and become in other tissues.
Having a single, as opposed to or.
A molecule or compound which can exist individually or serve as a building block or of a larger aggregate known as a. Polymers form when multiple monomers of the same or similar molecular species are connected to each other by chemical bonds, either in a linear chain or a non-linear conglomeration. Examples include the individual which form polymers, the individual which form, and the individual proteins which form.
Any of a class of organic compounds which are the simplest forms of and the most basic structural subunits or from which larger carbohydrate such as,, and are composed. With few exceptions, all monosaccharides are variations on the empirical formula, where typically ranges from 3 to 7. Common examples include,, and.
The abnormal and frequently pathological presence of only one of a normal pair. It is a type of.
A synthetic connecting a short sequence of into an artificial , used in to by with sequences in naturally occurring RNA or DNA molecules, especially, thereby inhibiting interactions with other biomolecules such as proteins and. Morpholino oligomers are not themselves, and neither they nor their hybrid duplexes with RNA are attacked by ; also, unlike the negatively charged of normal nucleic acids, the synthetic backbones of Morpholinos are electrically neutral, making them less likely to interact non-selectively with a host cell's charged proteins. These properties make them useful and reliable tools for artificially generating phenotypes in living cells.
The presence of two or more populations of cells with different in an individual organism which has developed from a single fertilized egg. A mosaic organism can result from many kinds of genetic phenomena, including of chromosomes,, or mutations in individual lineages during the early development of the embryo. Mosaicism is similar to but distinct from.
Any distinctive or recurring of in a or of in a that is or is conjectured to be biologically significant, especially one that is reliably by other biomolecules or which has a that permits unique or characteristic chemical interactions such as. In nucleic acids, motifs are often short, highly which act as recognition sites for or RNAs involved in the regulation of.
Any which converts chemical energy derived from the hydrolysis of such as and into mechanical work in order to effect its own locomotion, by propelling itself along a filament or through the.
See '.
See '.
Composed of more than one. The term is used especially to describe organisms or tissues consisting of many cells descendant from the same original which work together in an organized way, but may also describe groups of nominally single-celled organisms such as protists and bacteria which live symbiotically with each other in large colonies. Contrast '.
An aggregate of two or more molecular entities, identical or non-identical, held together by non-covalent forces; e.g. a.
Having more than one within a single ; i.e. having multiple nuclei occupying the same.
The integration of data from multiple "omics" technologies in order to study complex biological relationships, discover novel associations between biological entities, pinpoint relevant, or build elaborate models of physiology and disease.
A locus or sequence within a which contains multiple unique recognized by various, which makes it possible for scientists to target the of a DNA fragment specifically to that locus and in the desired orientation, by the insert and the vector with the same endonuclease and then them together via compatible restriction ends, a technique known as. Commercial plasmids designed for cloning commonly incorporate one or more multiple cloning sites.
Any physical or chemical agent that of an organism and thereby increases the frequency of above natural background levels.
1. The process by which the genetic information of an organism is changed, resulting in a. Mutagenesis may occur spontaneously or as a result of exposure to a.
2. In, any laboratory technique by which one or more genetic mutations are deliberately in order to produce a gene, regulatory element, gene product, or so that the functions of a genetic locus, process, or product can be studied in detail.
An organism, gene product, or phenotypic resulting from a, of a type that would not be observed naturally in specimens.
Any permanent change in the of a strand of or, or in the sequence of a. Mutations play a role in both normal and abnormal biological processes; their natural occurrence is integral to the process of. They can result from errors in, chemical damage, exposure to high-energy radiation, or manipulations by. mechanisms have evolved in many organisms to correct them. By understanding the effect that a mutation has on, it is possible to establish the function of the or sequence in which it occurs.
Any mutant or sequence that increases the spontaneous of one or more other genes or sequences. Mutators are often, or may be mutant such as those that encode or proteins involved in.
A , i.e. a protein whose sequence differs from that of the normal because of a.
The smallest unit of a DNA molecule in which a physical or chemical change can result in a .