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tolbutamide
A sulphonylurea that will bind to SUR and enhance insulin release from pancreatic B cells. Used in Type II diabetes (as are a number of similar drugs).
tolerance
The development of specific non-reactivity to an antigen. See immunological tolerance.
toll
Drosophila gene required for dorsoventral polarity determination. Protein (124 kD) is a transmembrane receptor with leucine-rich repeat. Interacts downstream with pelle and ...
toluidine blue
(= CI Basic Blue 17) A thiazin dye related to methylene blue and Azure A in structure; often used for staining thick resin sections. Typically exhibits metachromasia.
Tom complex
(= translocase of outer membrane) Transport complex of the outer membrane of mitochondrion. The complex contains eight different proteins: Tom40 (40 kD) forms the 2.2nm ...
tonic
See adaptation.
tonofilaments
Cytoplasmic filaments (10nm diameter: intermediate filaments) inserted into desmosomes.
tonoplast
Membrane that surrounds the vacuole in a plant cell.
tonoplast intrinsic protein
Plant protein, closely related to major intrinsic protein. Found in plant storage vacuolar membranes.
tophus
Mass of urate crystals surrounded by a chronic inflammatory reaction: characteristic of gout.
topographic map
The spatially ordered projection of neurons onto their target; eg. in the retino-tectal projection, retinal ganglion cell axons project along the optic nerve to the ...
topographical control
Those phenomena of cell behaviour in which the shape of the local substrate of the cell affects its behaviour, see for example contact guidance.
topoinhibition
Term used to describe the inhibition of cell proliferation as the cells become closely packed on a culture dish: generally superseded by the term density dependent inhibition.
topoisomerases
Enzymes that change the degree of supercoiling in DNA by cutting one or both strands. Type I topoisomerases cut only one strand of DNA; type I topoisomerase of E. coli (omega ...
TOR
(= target of rapamycin) Components of the ras/MAP kinase signalling pathway, originally characterized in yeast. Inhibited by rapamycin that is bound to FKBP12.
Torres body
Intranuclear inclusion body in liver cells infected with yellow fever virus (Togaviridae).
torso
A receptor tyrosine kinase (EC. 2.7.1.112) activated at the poles of the Drosophila embryo. Activation of torso triggers expression of gap genes that operate in these areas ...
torus
Structure found at the centre of a bordered pit, especially in conifers, forming a thickened region of the pit membrane. When subjected to a pressure gradient, it seals the pit ...
totipotent
Capable of giving rise to all types of differentiated cell found in that organism. A single totipotent cell could, by division, reproduce the whole organism.
toxic shock syndrome
Endotoxic shock caused by bacterial contamination of tampons; toxin responsible is produced by some strains of Staphylococcus aureus.
toxigenicity
The ability of a pathogenic organism to produce injurious substances that damage the host.
toxin
A naturally-produced poisonous substance that will damage or kill other cells. Bacterial toxins are frequently the major cause of the pathogenicity of the organism in question. ...
toxoid
Non-toxic derivative of a bacterial exotoxin produced by formaldehyde or other chemical treatment: useful as a vaccine because it retains most antigenic properties of the ...
Toxoplasma
A genus of parasitic protozoa. T. gondii is an intracellular parasite whose intermediate hosts includes humans, the final host being felines of many species. Causes ...
TP-1
See trophoblast protein 1.
TPA
(1) See tissue plasminogen activator. (2) A phorbol ester tumour promoter, 12-O-tetradecanoyl-phorbol-13-acetate also known as PMA, phorbol myristyl acetate.
TPCK
(= tosyl phenyl chloromethyl ketone) Nonspecific protease inhibitor, interacts with histidine residues and will inactivate many enzymes by interfering with the active site.
TphiCG loop
(= TfCG) See T-loop of RNA.
TPR motif
(= tetratricopeptide motif) Degenerate consensus sequence of 34 residues found in various proteins that are involved in the regulation of RNA synthesis, protein import and ...
trabecular bone
See cancellous bone.
tracheid
Water-conducting cell forming part of the plant xylem. Contains thick, lignified secondary cells walls, with no protoplast at maturity. Interconnects with neighbouring tracheids ...
TRADD
(= TNF-receptor-1 associated death domain protein) Binds to TNF-R cytoplasmic domain and to FADD and RIP though does not itself seem to have any catalytic activity. Contains a ...
TRAF
(= TNF receptor-associated protein) One of the various proteins that associates with the cytoplasmic domain of the TNF receptor.
TRAIL
(= TNF-related apoptosis-inducing ligand; Apo2L) An orphan member of the TNF ligand family that can be expressed either as a transmembrane protein (32 kD) or in soluble form; ...
tram
(= translocating chain-associating membrane protein) Transmembrane glycoprotein (probably crosses 8 times) of endoplasmic reticulum (36 kD) apparently required for the ...
TRAMP
(= DR3; wsl; Apo-3) Member of the death receptor family. Ligand not identified.
trans-Golgi network
A complex of membranous tubules and vesicles, near the trans -face of the Golgi apparatus, which is thought to be a major intersection for intracellular traffic of vesicles.
trans-splicing
(of RNA) Splicing of two different pre-mRNA molecules together. Seems to rely on intron-like sequences. Contrasts with the normal cis -splicing of conventional RNA molecules.
transactivation
Stimulation of transcription by a transcription factorbinding to DNA and activating adjacent proteins.
transacylase
An enzyme that transfers an acyl group; eg. transacetylase that transfers an acetyl group from acetyl-lipoamide to coenzyme A.
transaldolase
Together with transketolase, links the pentose phosphate pathway with glycolysis by converting pentoses to hexoses.
transaminases
Enzymes that convert amino acids to keto acids in a cyclic process using pyridoxal phosphate as cofactor; eg. aspartate amino transferase catalyses the reaction: aspartate ...
transcriptase
See reverse transcriptase.
transcription
Synthesis of RNA by RNA polymerases using a DNA template.
transcription factor
Protein required for recognition by RNA polymerases of specific stimulatory sequences in eukaryotic genes. Several are known that activate transcription by RNA polymerase II ...
transcription squelching
Anomalous suppression of transcription of a gene by overexpression of a transcription factor that would be expected to raise transcription levels. Thought to be caused by ...
transcription unit
A region of DNA that is transcribed to produce a single primary RNA transcript, ie. a newly synthesized RNA molecule that has not been processed. Transcription units can be ...
transcriptional control
Control of gene expression by controlling the number of RNA transcripts of a region of DNA. A major regulatory mechanism for differential control of protein synthesis in both ...
transcriptional silencing
Mechanism of transcriptional control where DNA is bundled into heterochromatin in order to make it permanently inaccessible for future transcription. Effectively, this allows ...
transcytosis
Process of transport of material across an epithelium by uptake on one face into a coated vesicle, which may then be sorted in the endosomal compartment, and then delivery to ...
transcytotic vesicle
Membrane-bounded vesicle that shuttles fluid from one side of the endothelium to the other. There is some controversy as to whether or not they form pores.
transdetermination
Change in determined state observed in experiments on Drosophila imaginal discs. These can be cultured for many generations in the abdomen of an adult, where they proliferate ...
transdifferentiation
Change of a cell or tissue from one differentiated state to another. Rare, and has mainly been observed with cultured cells. In newts the pigmented cells of the iris ...
transducin
A GTP-binding protein found in the disc membrane of retinal rods and cones: of the part of the cascade involved in transduction of light to a nervous impulse. A complex of ...
transduction
(1) The transfer of a gene from one bacterium to another by a bacteriophage. In generalized transduction any gene may be transferred as a result of accidental incorporation ...
transfection
The introduction of DNA into a recipient eukaryote cell and its subsequent integration into the recipient cell\'s chromosomal DNA. Usually accomplished using DNA precipitated ...
transfer cell
Parenchyma cell specialized for transfer of water-soluble material to or from a neighbouring cell, usually a phloem sieve tube or a xylem tracheid. Elaborate wall ingrowths ...
transfer factor
A dialysable factor obtained from sensitised T-cells by freezing and thawing, that may possibly immunopotentiate animals. The transfer of specific immunity from one animal to ...
transfer RNA
See tRNA.
transferase
A suffix to the name of an enzyme indicating that it transfers a specific grouping from one molecule to another; eg. acyl transferases transfer acyl groups.
transferrin
The iron storage protein (80 kD) found in mammalian serum; a b-globulin. Binds ferric iron with a Kass of around 21 at pH 7.4, 18.1 at pH 6.6. An important constituent of growth ...
transformasome
Membranous extension responsible for binding and uptake of DNA; found on the surface of transformation-competent Haemophilus influenzae bacteria.
transformation
Any alteration in the properties of a cell that is stably inherited by its progeny. Classical example was the transformation of Diplococcus pneumoniae to virulence by DNA, ...
transformed cell
See transformation.
transforming genes
Genes, originally of tumour viruses, responsible for their ability to transform cells. The term now serves as an operational definition of oncogenes.
transforming growth factor
Proteins secreted by transformed cells that can stimulate growth of normal cells. Unfortunate misnomer, since they induce aspects of transformed phenotype, such as growth in ...
transforming virus
Viruses capable of inducing malignant transformation of animal cells in culture. Among the Oncovirinae, non-defective viruses that lack oncogenes can induce tumours such as ...
transgelin
Transformation and shape-change sensitive isoform of 21 kD actin binding protein. Highly conserved (as far back as yeast), binds F-actin (1:6 transgelin:G-actin) and causes ...
transgene
A gene or DNA fragment from one organism that has been stably incorporated into the genome of another organism (usually plant or animal).
transgenic
Adjective describing an organism (usually plant or animal) that contains a transgene.
transgenic organisms
Organisms that have integrated foreign DNA into their germ line as a result of the experimental introduction of DNA.
transglutaminase
An important extracellular enzyme that catalyses the formation of an amide bond between side-chain glutamine and side-chain lysine residues in proteins with the elimination of ...
transglycosylation
Transfer of a glycosidically bound sugar to another hydroxyl group.
transhydrogenase
Direct transfer of a hydrogen atom from NADH to NADPH as catalysed by enzymes in mitochondria from liver or heart.
transient expression
(= transient transfection) When transfecting animal cells, cells in which the transgene has not been physically incorporated into the genome (stable transfection), but is ...
transin
Protease secreted by carcinoma cells: carboxy-terminal domain has distant homology to haemopexin (haem binding protein), and the N-terminal domain has the proteolytic activity. ...
transition probability model
A model to account for the apparently random variation in cell cycle time between individual animal tissue cells in culture, that postulates that transition from G1 to S phase ...
transition proteins
In spermatogenesis, group of proteins that displace histones from nuclear DNA, and that are in turn displaced by protamines to produce the transcriptionally inactive nuclear ...
transition temperature
The temperature at which there is a transition in the organization of, for example, the phospholipids of a membrane where the transition temperature marks the shift from fluid to ...
transitional elements
Region at the boundary of the rough endoplasmic reticulum (RER) and the Golgi. Transport vesicles are responsible for the transfer of secretory proteins from this part of the ...
transitional endoplasmic reticulum
See transitional elements.
transitional epithelium
An epithelial sheet made up of cells that change shape when the epithelium is stretched. Usually a stratified epithelium: best known example is in the bladder
transketolase
See transaldolase.
translation
The process that occurs at the ribosome whereby the information in mRNA is used to specify the sequence of amino acids in a polypeptide chain.
translational control
Control of protein synthesis by regulation of the translation step, for example by selective usage of preformed mRNA or instability of the mRNA.
translocase
(= elongation factor G; EF-G) The enzyme that causes peptidyl-tRNA to move from the A-site to the P-site in the ribosome and the mRNA to move so that the next codon is in ...
translocating chain-associating membrane protein
(= TRAM) Transmembrane glycoprotein (probably crosses 8 times) of endoplasmic reticulum (36 kD) apparently required for the translocation of nascent proteins into the ...
translocation
Rearrangement of a chromosome in which a segment is moved from one location to another, either within the same chromosome or to another chromosome. This is sometimes ...
translocon
The complex of proteins associated with the translocation of nascent polypeptides into the cisternal space of the endoplasmic reticulum. The translocon is a multi-functional ...
transmembrane protein
A protein subunit in which the polypeptide chain is exposed on both sides of the membrane. The term does not apply when different subunits of protein complex are exposed at ...
transmembrane transducer
A system that transmits a chemical or electrical signal across a membrane. Usually involves a transmembrane receptor protein that is thought to undergo a conformation change that ...
transmigration
Migration of cells from one surface of a monolayer of cells to the other side; used particularly of the migration of leucocytes from the lumen of a blood vessel across ...
transmissible mink encephalopathy
One of the transmissible spongiform encephalopathies, though originally thought to be an ‘unconventional’ type of slow virus infection. Similar to kuru, scrapie, and ...
transmission electron microscopy
Those forms of electron microscopy in which electrons are transmitted through the object to be imaged, suffering energy loss by diffraction and to a small extent by absorption. ...
transpeptidase
An enzyme that catalyses the formation of an amide linkage between a free amino group and a carbonyl group within an existing peptide linkage.
transpiration
Loss of water-vapour from land-plants into the atmosphere, causing movement of water through the plant from the soil to the atmosphere via roots, shoot and leaves. Occurs mainly ...
transplantation antigen
Any antigen that is antigenically active in graft rejection. In practice the major histocompatibility complex and the H-Y antigens, and to a lesser extent minor ...
transplantation reaction
The set of cellular phenomena observed after an allogeneic (mismatched) graft is made to an organism that leads to destruction, detachment or isolation of the graft. In mammals ...
transport diseases
Single-gene defect diseases in which there is an inability to transport particular small molecules across membranes. Examples are aminoacidurias such as cystinuria, ...
transport protein
A class of transmembrane protein that allows substances to cross plasma membranes far faster than would be possible by diffusion alone. A major class of transport proteins ...
transport vesicle
Vesicles that transfer material from the rough endoplasmic reticulum (RER) to the receiving face of the Golgi.
transportase
See transport protein.
transporter
See transport protein.
transportin
Component (101 kD) of the nuclear pore complex. Exports RNA from the nucleus (whereas yeast counterpart, Kap104p, imports).
transposable element
See transposon.
transposase
See transposon.
transposition
Movement form one location to another, particularly the movement of a DNA sequence (transposon) within the genome.
transposon
(= transposable element) Small, mobile DNA sequences that can replicate and insert copies at random sites within chromosomes. They have nearly identical sequences at each end, ...
transthyretin
Plasma protein (4.5mM in plasma) that transports thyroxine. Tetrameric with 4 identical 127-residue subunits. Transthyretin forms a complex under physiological conditions with ...
transudate
Plasma-derived fluid that accumulates in tissue and causes oedema. A result of increased venous and capillary pressure, rather than altered vascular permeability (which leads ...
transverse tubule
See T tubule.
transversions
Point mutation in which a purine is substituted by a pyrimidine or vice versa.
tre
Human oncogene probably encoding a transcription factor.
TRE
(= thyroid hormone response element) DNA sequence recognized by the thyroid hormone receptor.
treadmilling
Name given to the proposed process in microtubules in which there is continual addition of subunits at one end, and disassembly at the other, so that the tubule stays of ...
trefoil motif
(= P domain) Domain found in various secretory polypeptides that has highly conserved cysteine residues that are disulphide bonded in such a way as to generate a trefoil ...
trehalose
A disaccharide sugar (342 D) found widely in invertebrates, bacteria, algae, plants and fungi, formed by the dimerisation of glucose. Yields glucose on acid hydrolysis.
trephones
Substance supposedly released at a wound that stimulate mitosis: the opposite of chalones.
Treponema
Genus of bacteria of the spirochaete family (Spirochaetaceae). T. pallidum causes syphilis. Cells are corkscrew-like, (6-15 mкm long, 0.1-0.2 mкm wide), motile, anaerobic, ...
TRF
Alternative name for thyrotropin-releasing hormone.
TRF1
(= telomerase repeat binding factor 1) Major protein component (33 kD) of telomeres, co-localizes with telomeres in interphase and is located at chromosome ends during ...
triacyl glycerols
See triglycerides.
triad
(= triad junction) The junction between the T tubules and the sarcoplasmic reticulum in striated muscle.
tricarboxylic acid cycle
(= TCA cycle; citric acid cycle; Krebs cycle) The central feature of oxidative metabolism. Cyclic reactions whereby acetyl CoA is oxidized to carbon dioxide providing ...
trichocyst
Small membrane-bounded vesicle lying below the pellicle of many ciliates. Fusion of the trichocyst with the plasma membrane occurs at a predictable site which can therefore be ...
trichohyalin
Major structural protein of inner root sheath cells and medulla of hair follicle, present in small amounts in other specialised epithelia. Trichohyalin is a high molecular ...
Trichonympha
Genus of flagellated protozoans symbiotic in the intestine of some cockroaches and termites where they are responsible for the digestion of cellulose.
trichothecenes
(= T-2 toxin; HT-2 toxin; diacetoxyscirpenol; deoxynivalenol) Mycotoxins produced by various species of fungi that contaminate various agricultural products. Are toxic for ...
triflavin
See disintegrin.
trifluoperazine
(= TFP; trifluperazine; Stellazine) Antipsychotic drug that inhibits calmodulin at levels just below those at which it kills cells.
trigeminal system
Neurons associated with the fifth or trigeminal nerve, the largest cranial nerve. The trigeminal system provides sensory innervation to the face and mucous membrane of the oral ...
trigger protein
See U protein.
triglycerides
Storage fats of animal adipose tissue where they are largely glycerol esters of saturated fatty acids. In plants they tend to be esters of unsaturated fatty acids (vegetable ...
trigramin
See disintegrin.
trimethoprim
A drug that inhibits the reduction of dihydrofolate to tetrahydrofolate (a later step than that inhibited by sulphonamides). Selective for some bacterial DHF reductases and ...
trinucleotide repeat
Repetitive part of a genome that may form part of the coding sequence of a gene. The length of such repeats is frequently polymorphic, and unstably amplified repeats appear to ...
trio
Multidomain protein (2861 residues) that binds LAR transmembrane tyrosine phosphatase, has a serine/threonine protein kinase domain and separate rac- and rho-specific ...
triodobenzoic acid
(= TIBA) An inhibitor of basipetal auxin transport in plants.
triple response
The vascular changes in the skin in response to mild mechanical injury, an outward-spreading zone of reddening (flare) followed rapidly by a weal (swelling) at the site of ...
triploid
Having three times the haploid number of chromosomes.
triskelion
A three-legged structure assumed by clathrin isolated from coated vesicles. A trimer of clathrin (180 kD) with three light chains is probably the physiological subunit of ...
trisomy
An additional copy of a chromosome so that there are three copies not two in a diploid organism. Best known example is trisomy 21 in Down\'s syndrome.
tritium
(= 3H;H) Long-lived radioactive isotope of hydrogen (half-life 12.26 years). Weak b -emitter, very suitable for autoradiography, and relatively easy to incorporate into complex ...
Triton X-100
Non-ionic detergent used in isolating membrane proteins: the detergent replaces the phospholipids that normally surround such a protein. Other detergents of the Triton group are ...
Triturus
Genus of newts, much studied for their lampbrush chromosomes.
trk
Oncogene, from human colon carcinoma, encoding a receptor tyrosine kinase. The trk gene product is a receptor for NGF, that of the trkB gene the receptor for neurotrophin 4 ...
tRNA
(= transfer RNA; s-RNA; 4S RNA) The low molecular weight RNAs that specifically bind amino acids by amino-acylation to form aminoacyl tRNA, and that possess a special ...
trochophore
Free-living ciliated larval form of several different invertebrate phyla.
diabetes insipidus
Rare form of diabetes in which the kidney tubules do not reabsorb enough water. This can be because (a) either the renal tubules have defective receptors for antidiuretic ...
diabetes mellitus
Relative or absolute lack of insulin leading to uncontrolled carbohydrate metabolism. In juvenile onset diabetes (that may be an autoimmune response to pancreatic B cells) the ...
diabetes related peptide
See islet amyloid peptide.
diacetoxyscirpenol
Trichothecene mycotoxin produced by various species of fungi. Cytotoxic for human CFU-GM and BFU-E.
diacylglycerol
Glycerol substituted on the 1 and 2 hydroxyl groups with long chain fatty acyl residues. DAG is a normal intermediate in the biosynthesis of phosphatidyl phospholipids and is ...
diacytosis
Discharge of an empty pinocytotic vesicle from a cell. Not commonly used.
diakinesis
The final stage of the first prophase of meiosis. The chromosomes condense to their greatest extent during this stage and normally the nucleolus disappears and the fragments ...
dialysis
Separation of molecules on the basis of size through a semi-permeable membrane. Molecules with dimensions greater than the pore diameter are retained inside the dialysis bag or ...
diaminobenzidine
Peroxidase substrate - but a potent carcinogen.
diaminobenzoic acid
(= DABA; 3,5-diaminobenzoic acid) Compound used in fluorimetric determination of DNA content: gives fluorescent product when heated in acid solution with aldehydes.
diapedesis
Archaic term for the emigration of leucocytes across the endothelium.
diaphorase
Any enzyme capable of catalysing oxidation of NAD or NADPH in the presence of an electron acceptor other than oxygen - for example methylene blue, quinones or cytochromes. ...
diatom
Algae of the division Bacillariophyta; largely unicellular and characterized by having cell walls of hydrated silica embedded in an organic matrix. The cell walls are formed in ...
dibutyryl cyclic AMP
An analogue of cyclic AMP that shares some of the pharmacological effects of this nucleotide, but is generally believed to enter cells more readily on account of its greater ...
dichlorobenzonitrile
(= 2,6-dichlorobenzonitrile) Inhibitor of cellulose biosynthesis in higher plants.
dichlorophenoxyacetic acid
(= 2,4-dichlorophenoxyacetic acid; 2,4-D) A synthetic auxin, also used as a selective herbicide.
dichroism
See circular dichroism.
dickkopf-1
(= dkk-1) Gene in Xenopus that encodes a secreted protein (259 residues, 40 kD) that induces the head region in the developing embryo. Member of a family of genes. Dkk-1 is a ...
dicotyledonous plants
Plants belonging to the large subclass of Angiosperms that have two seed-leaves (cotyledons). Includes the majority of herbaceous flowering plants and most deciduous woody plants ...
dictyosome
Organelle found in plant cells and functionally equivalent to the Golgi apparatus of animal cells.
Dictyostelium
A genus of the Acrasidae, the cellular slime moulds.
dictyotene
Prolonged diplotene of meiosis: the stage at which oocyte nuclei remain during yolk production.
dideoxy sequencing
(= Sanger dideoxy sequencing) The most popular method of DNA sequence determination (cf. Maxam-Gilbert method). Starting with single-stranded template DNA, a short ...
Diels-Alder reaction
Reaction used in organic synthesis of six-membered rings.
diencephalon
In vertebrate central nervous system, the most rostral part of the brain stem, consisting of the thalamus, hypothalamus, subthalamus and epithalamus. It is a key relay zone for ...
differential adhesion
The differential adhesion hypothesis was advanced by Steinberg to explain the mechanism by which heterotypic cells in mixed aggregates sort out into isotypic territories. ...
differential display PCR
Variation of the polymerase chain reaction used to identify differentially expressed genes. mRNA from two different tissue samples is reverse transcribed, then amplified using ...
differential interference contrast
Method of image formation in the light microscope based on the method proposed by Nomarski (though strictly speaking all forms of optical microscopy rely to a greater or lesser ...
differential scanning calorimetry
Form of thermal analysis in which heat flows to a sample and a standard at the same temperature are compared, as the temperature is changed.
differential screening
General term for techniques used to identify genes that are expressed differentially in two different conditions. These are usually based on identifying those mRNAs that are more ...
differentiation
Process in development of a multicellular organism by which cells become specialized for particular functions. Requires that there is selective expression of portions of the ...
differentiation antigen
Any large structural macromolecule that can be detected by immune reagents and that also is associated with the differentiation of a particular cell type or types. Many cells ...
differentiation factors
Members of the TGF- b family of growth factors. See also midkine.
diffraction
When a wave-train passes an obstacle secondary waves are set up that interfere with the primary wave and give rise to bands of constructive and destructive interference. Around a ...
diffusion coefficient
(= diffusion constant) For the translational diffusion of solutes, diffusion is described by Fick\'s First Law, that states that the amount of a substance crossing a given area ...
diffusion limitation
The boundary layer hypothesis; that the proliferation of cells in culture is limited by the rate at which some essential component (almost certainly a growth factor) diffuses ...
diffusion potential
Potential arising from different rates of diffusion of ions at the interface of two dissimilar fluids; a junction potential.
DiGeorge syndrome
Congenital absence of the thymus and parathyroid as a result of which the T-lymphocyte system is absent.
digestive vacuole
Intracellular vacuole into which lysosomal enzymes are discharged and digestion of the contents occurs. More commonly referred to as a secondary lysosome.
digitalis
General term for pharmacologically active compounds from the foxglove ( Digitalis ). The active substances are the cardiac glycosides, digoxin, digitoxin, strophanthin and ...
digitonin
See saponin.
digoxygenin
Small molecule derived from foxgloves, that is used for labelling DNA or RNA probes, and subsequent detection by enzymes linked to anti-digoxygenin antibodies. Proprietary to ...
dihydroepiandrosterone
(= DHEA) Predominant androgen secreted from the adrenal cortex, an intermediate in androgen and oestrogen biosynthesis. Can be converted to sulphate (DHEA-S) the ...
dihydrofolate reductase
(= DHFR) An enzyme (EC 1.5.1.3) involved in the biosynthesis of folic acid coenzymes, that transfers hydrogen from NADP to dihydrofolate, yielding tetrahydrofolic acid, an ...
dihydropyridines
Specific blockers of some types of calcium channel, eg. nifedipine and nitrenidine.
DiI
Name used for fluorescent derivatives of indocarbocyanine iodide that have two long alkyl chains and are membrane soluble. Used as general stains for membranes and also as ...
dilution cloning
Cloning by diluting the cell suspension to the point at which the probability of there being more than one cell in the inoculum volume is small. Inevitably on quite a few ...
dinitrophenol
(= 2,4-dinitrophenol) A small molecule used as an uncoupler of oxidative phosphorylation. Also used after reaction with various proteins to provide a strong and specific ...
dinoflagellates
Photosynthetic organisms of the order Dinoflagellida (for botanists Dinophyceae). They are aquatic and abundant in marine plankton; two flagella lie in grooves in an often ...
dioecious
Flowering plants in which the sexes are separate; each plant is either male or female and flowers have either stamens or pistils but not both.
diphtheria toxin
An AB exotoxin (62 kD) coded by b corynephage of virulent Corynebacterium diphtheriae strains (that can produce a repressor of toxin production). The B subunit binds to ...
diplococcus
Bacterial strain in which two spherical cells (cocci) are joined to form a pair like a dumb-bell or figure-of-eight.
diploid
A diploid cell has its chromosomes in homologous pairs, and thus has 2 copies of each autosomal genetic locus. The diploid number (2n) equals twice the haploid number and is ...
diplornavirus
Proposed family of all double-stranded RNA viruses: considered taxonomically unsound by many virologists.
diplotene
The final stage of the first prophase of meiosis. All four chromatids of a tetrad are fully visible and homologous chromosomes start to move away from one another except at ...
Diptera
Order of insects with one pair of wings, the second pair being modified into balancing organs, the halteres; the mouthparts are modified for sucking or piercing. The insects show ...
diptericins
Inducible glycine-rich antibacterial peptides (about 8 kD) from Dipteran haemolymph.
direct B-cells
Lymphocytes responding to a small range of antigens by antibody production without any requirement for T-cells. The antigens include flagellin and pokeweed mitogen.
disaccharide
Sugar formed from two monosaccharide units linked by a glycosidic bond. The trehalose type are formed from two non-reducing sugars, the maltose type from two reducing ...
DISC
(= death-inducing signalling complex) See death-effector domain.
disc gel
Confusingly, nothing to do with shape; gels in which there is a discontinuity in pH, or gel concentration, or buffer composition.
discodermolide
Anti-tumour drug (a poly-hydroxylated alkatetraene lactone) that, like taxol, promotes formation of stable bundles of microtubules and competes with taxol for binding to ...
discoidin
A lectin, isolated from the cellular slime mould Dictyostelium discoideum (see Acrasidae), that has a binding site for carbohydrate residues related to galactose. The ...
disintegrins
Peptides found in the venoms of various snakes of the viper family, that inhibit the function of some integrins of the b 1 and b 3 classes. They were first identified as ...
disjunction mutant
Drosophila mutant in which chromosomes are partitioned unequally between daughter cells at meiosis, as a result of nondisjunction.
dispase
Trade name for a crude protease preparation used for disaggregating tissue in setting up primary cell cultures. Dispase gives less complete disaggreagtion than trypsin but ...
dispersion forces
Forces of attraction between atoms or non-polar molecules that result from the formation of induced dipoles. Sometimes referred to as London dispersion forces. Important in the ...
disseminated intravascular coagulation
Complication of septic shock in which endotoxin (from Gram negative bacteria) induces systemic clotting of the blood, probably indirectly through the effect of endotoxin on ...
dissociation
Any process by which a tissue is separated into single cells. Enzymic dissociation with trypsin or other proteases is often used.
dissociation constant
In a chemical equilibrium of form A + B = AB, the equilibrium concentrations (strictly, activities) of the reactants are related such that A x B/AB = a constant, Kd, the ...
distemper virus
Paramyxovirus of the genus Morbillivirus. Commonest is the canine distemper virus that causes fever, vomiting and diarrhoea; variant that infects seals (Phocavirus) has caused ...
disulphide bond
The -S-S- linkage. A linkage formed between the SH groups of two cysteine moieties either within or between peptide chains. Each cysteine then becomes a half-cystine residue. ...
dithioerythritol
Like dithiothreitol is also referred to as Cleland&’s reagent and has same properties.
dithiothreitol
(= Cleland\'s reagent) Used to protect sulphydryl groups from oxidation during protein purification procedures or to reduce disulphides to sulphydryl groups.
diurnal
Occurring during the day or repeating on a daily basis. Use of circadian rhythm for the latter avoids ambiguity.
division septum
The cell wall that forms between daughter cells at the end of mitosis in plant cells or just before separation in bacteria.
dizygotic
Twins arising as a result of the fertilization of two ova by two spermatozoa and thus genetically non-identical, in contrast to monozygotic twins.
DLVO theory
Theory of colloid flocculation advanced independently by Derjaguin & Landau and by Vervey & Overbeek and subsequently applied to cell adhesion. There exist distances (primary ...
DMARD
Disease Modifying Anti-Rheumatic Drug. Drug used for treating rheumatoid arthritis that does more than relieve symptoms. Examples include gold, penicillamine, sulphasalazine ...
DMEM
(= Dulbecco Modified Eagle&’s Medium) Very commonly used tissue culture medium for mammalian cells.
DMSO
Dimethyl sulphoxide. Much used as a solvent for substances that do not dissolve easily in water and that are to be applied to cells (for example cytochalasin B, formyl ...
DNA
(= deoxyribonucleic acid) The genetic material of all cells and many viruses. A polymer of nucleotides. The monomer consists of phosphorylated 2-deoxyribose N-glycosidically ...
DNA annealing
The reformation of double-stranded DNA from thermally denatured DNA. The rate of reassociation depends upon the degree of repetition, and is slowest for unique sequences (this is ...
DNA fingerprinting
See restriction fragment length polymorphism.
DNA footprinting
Technique for identifying the recognition site of DNA-binding proteins: see footprinting.
DNA glycosylase
(= DNA glycosidase) Class of enzymes involved in DNA repair. They recognize altered bases in DNA and catalyse their removal by cleaving the glycosidic bond between the base ...
DNA gyrase
A type II topoisomerase of Escherichia coli, that is essential for DNA replication. This enzyme can induce or relax supercoiling.
DNA helicase
(= unwindase) An enzyme that uses the hydrolysis of ATP to unwind the DNA helix at the replication fork, to allow the resulting single strands to be copied. Two molecules of ...
DNA hybridization
See hybridization.
DNA iteron
Repeated DNA sequence found near the origin of replication of some plasmids.
DNA library
See genomic library.
DNA ligase
Enzyme involved in DNA replication. The DNA ligase of E. coliseals nicks in one strand of double-stranded DNA, a reaction required for linking precursor fragments during ...
DNA methylation
Process by which methyl groups are added to certain nucleotides in genomic DNA. This affects gene expression, as methylated DNA is not easily transcribed. The degree of ...
DNA polymerases
Enzymes (EC 2.7.7.7) involved in template-directed synthesis of DNA from deoxyribonucleotide triphosphates. I, II and III are known in E. coli ; III appears to be most important ...
DNA rearrangement
Wholesale movement of sequences from one position to another in DNA, such as occur somatically, for example in the generation of antibody diversity.
DNA renaturation
See DNA annealing.
DNA repair
Enzymic correction of errors in DNA structure and sequence that protects genetic information against environmental damage and replication errors.
DNA replication
The process whereby a copy of a DNA molecule is made, and thus the genetic information it contains is duplicated. The parental double stranded DNA molecule is replicated ...
DNA sequence analysis
Determination of the nucleotide sequence of a length of DNA. Typically, this is performed by cloning the DNA of interest, so that enough can be prepared to allow the sequence ...
DNA synthesis
The linking together of nucleotides (as deoxyribonucleotide triphosphates) to form DNA. I n vivo, most synthesis is DNA replication, but incorporation of precursors also occurs ...
DNA topoisomerase
An enzyme capable of altering the degree of supercoiling of double-stranded DNA molecules. Various topoisomerases can increase or relax supercoiling, convert single-stranded ...
DNA transfection
A technique originally developed to allow viral infection of animal cells by uptake of purified viral DNA rather than by intact virus particles. Term, a hybrid between ...
DNA tumour virus
Virus with DNA genome that can cause tumours in animals. Examples are Papovaviridae, Adenoviridae and Epstein-Barr virus.
DNA virus
Lackie A virus in which the nucleic acid is double- or single-stranded DNA (rather than RNA). Major groups of double-stranded DNA viruses are papovaviruses, adenoviruses, ...
DNA-binding proteins
Proteins that interact with DNA, typically to pack or modify the DNA eg. histones, or to regulate gene expression, transcription factors. Among those proteins that recognize ...
dnaA etc.
Genes in E. coli that are involved in coding for replication machinery. dnaA and P produce proteins involved in replication at the chromosome origin; dnaB, C and D are ...
DNAase
See deoxyribonuclease.
docking protein
See signal recognition particle-receptor.
dolichol
Terpenoids with 13-24 isoprene units and a terminal phosphorylated hydroxyl group. Function as transmembrane carriers for glycosyl units in the biosynthesis of glycoproteins and ...
domain
Used to describe a part of a molecule or structure that shares common physicochemical features, eg. hydrophobic, polar, globular, a -helical domains, or properties eg. ...
dominant negative
A mutation which is capable of exerting an effect even when only one copy is present, as in a heterozygote. Usually explained as a mutation that disrupts one subunit of a ...
domoic acid
An excitatory amino acid transmitter.
Donnan equilibrium
An equilibrium established between a charged, immobile colloid (such as clay, ion exchange resin or cytoplasm) and a solution of electrolyte. Characteristics: ions of like charge ...
donor splice junction
The junction between an exon and an intron at the 5\' end of the intron. When the intron is removed during processing of hnRNA the donor junction is spliced to the acceptor ...
DOPA
(= L-DOPA; levodopa; 3-hydroxytyrosine) Precursor of the neurotransmitter dopamine, made from L-tyrosine by tyrosine 3-mono-oxygenase and used as a treatment for Parkinsonism. ...
dopamine
A catecholamine neurotransmitter and hormone (153 D), formed by decarboxylation of dehydroxyphenylalanine (DOPA). A precursor of adrenaline and noradrenaline.
dorsal
Drosophila polarity gene; homologue of the rel proto-oncogene. See tube, pelle and toll.

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