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 (0–L) lists terms beginning with numbers and those beginning with the letters A through L. Glossary of cellular and molecular biology (M–Z) (this page) lists terms beginning with the letters M through Z.
This glossary is intended as introductory material for novices (for more specific and technical detail, see the article corresponding to each term). 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.
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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 (1) 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 (i.e. a micelle). 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 (e.g. individual and , , organic acids, amines, , , , etc.) and molecules (e.g. drugs, toxins, environmental contaminants, and other xenobiotics).
(of a linear or chromosome fragment) 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 (ranging in length from one to six or more ) 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 (VNTR) 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 (nm) to 100 micrometres (μm) 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 (as with and ). 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.