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 page, Glossary of cellular and molecular biology (0–L), lists terms beginning with numbers and with the letters A through L. Glossary of cellular and molecular biology (M–Z) 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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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 (i.e. the terminus at which the 3' carbon is not attached to another nucleotide via a ; , the 3' carbon is often still bonded to a hydroxyl group). By convention, sequences and structures positioned nearer to the 3'-end relative to others are referred to as . Contrast .
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 (i.e. the terminus at which the 5' carbon is not attached to another nucleotide via a ; , the 5' carbon is often still bonded to a group). By convention, sequences and structures positioned nearer to the 5'-end relative to others are referred to as . Contrast .
See .
A
(of a linear or chromosome fragment) 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 .
(of a linear or chromosome fragment) 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 (commonly three or four) 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 (such as a or ) across a against a concentration gradient. Unlike , active transport requires an expenditure of energy.
The covalent attachment of any acyl group (e.g. acetyl or benzoyl) 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 (e.g. ); it is also the primary conformation adopted by and .Ussery, David W. "DNA Structure: A-, B-, and Z-DNA Helix Families". Lyngby, Denmark: Danish Technical University.
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.
Any (especially a drug or hormone) that in binding to or interacting with a protein causes a that converts the receptor into an active form, thereby initiating a biological response. In contrast, an has the opposite effect on the receptor, inactivating or disabling it, while an competes with or directly blocks the agonist, preventing it from activating the receptor.
A laboratory method used in molecular biology to extract and isolate such as the DNA of (as opposed to ) 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.
See .
Any of a set of enzymes which catalyze the transesterification reaction that results in the attachment of a specific (or a precursor) 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 (e.g. by spontaneous ) or artificially (e.g. by ), 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 (creating a ) while the other has one or more extra copies of the same chromosomes (creating a ).
(of a linear or chromosome fragment) 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 (but excluding abnormal numbers of complete sets of chromosomes, which instead is known as ).