| G+C ratio | <molecular biology> In DNA (or RNA) from any organism, the percent of the total nucleic acid that consists of guanine plus cytosine bases. (20 Mar 1998) |
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| g-6-p-d deficiency | <biochemistry> An inherited condition that results in a deficiency in glucose-6-phosphate dehydrogenase. Particular drugs (sulphonamides) can exacerbate this problem. The result is haemolytic anaemia. (27 Sep 1997) |
| G-banding | <genetics> Chromosomes stained with certain dyes, commonly quinacrine (Q banding) or Giemsa (G banding), show a pattern of transverse bands of light and heavy staining that is characteristic for the individual chromosome. The basis of the differential staining, which is the same in most tissues, is not understood: each band represents 5-10% of the length, about 10exp7 base pairs, although this is not true for polytene chromosomes in Drosophila that show more than 4000 bands. (18 Nov 1997) |
| G-banding stain | <technique> A unique chromosome staining technique, used in human cytogenetics to identify individual chromosomes, which produces characteristic bands. It utilises acetic acid fixation, air drying, denaturing chromosomes mildly with proteolytic enzymes, salts, heat, detergents, or urea, and finally Giemsa stain; chromosome bands appear similar to those fluorochromed by Q-banding stain. Synonym: Giemsa chromosome banding stain. (05 Mar 2000) |
| G-CSF | <growth factor, haematology, oncology> A glycoprotein of 25 kD containing internal disulfide bonds. It induces the survival, proliferation, and differentiation of neutrophilic granulocyte precursor cells and functionally activates mature blood neutrophils. Among the family of colony-stimulating factors, G-CSF is the most potent inducer of terminal differentiation to granulocytes and macrophages of leukaemic myeloid cell lines. A protein that stimulates the growth and maturation of granulocytes. It is used to promote the recovery of the white cells following chemotherapy. See: colony-stimulating factor. Acronym: G-CSF (12 Dec 1998) |
| G-protein | <cell biology, molecular biology> Intracellular membrane-associated proteins activated by several (e.g., beta adrenergic) receptors. They serve as second messengers or transducers of the receptor-initiated response to intracellular elements such as enzymes to initiate an effect. They are also mediators of activated cell-surface receptors and their enzymes or of ion channels. They are responsible for activating a chain of events that alters the concentration of intracellular signaling molecules such as cyclic AMP and calcium. In turn, these intracellular messengers alter the behaviour of other target proteins within the cell. These proteins have a high affinity for guanine nucleotides and hence are named "G" proteins. Synonym: G-protein, GTP-binding proteins. (12 Jul 2000) |
| G-protein coupled receptor | <cell biology> Cell surface receptors that are coupled to G-proteins (GTP-binding protein). G-protein coupled receptors are thought to have seven membrane spanning domains and have been divided into 2 subclasses: those in which the binding site is in the extracellular domain for example receptors for glycoprotein hormones, such as thyroid stimulating hormone (TSH) and follicle-stimulating hormone (FSH) and those in which the ligand binding site is likely to be in the plane of the 7 transmembrane domains for example rhodopsin and receptors for small neurotransmitters and hormones for example muscarinic acetylcholine receptor. (18 Nov 1997) |
| G-protein, inhibitory GI | A g-protein that inhibits adenylyl cyclase and activates k+ channels. (12 Dec 1998) |
| G-protein, stimulatory gs | A G-protein that mediates the receptor activation of adenylyl cyclase. (12 Dec 1998) |
| G-strophanthin | <drug> A plant alkaloid from Strophantus gratus, that specifically binds to and inhibits the sodium potassium ATPase. Related to digitalis. (18 Nov 1997) |
| g0 phase | Phase of the cell cycle where cells exist in a quiescent state. These cells have unduplicated DNA, degraded RNA and protein, and low enzyme activity. The ability to switch between g0 and g1 (and vice versa) determines the post-embryonic cell proliferation rate and is defectively controlled in neoplastic cells. (12 Dec 1998) |
| G1 | Symbol for gap 1. (05 Mar 2000) |
| g1 phase | <cell biology, molecular biology> The period during interphase in the cell cycle between mitosis and the S phase (when DNA is replicated). Also known as the decision period of the cell, because the cell decides to divide when it enters the s phase. The G stands for gap. (09 Oct 1997) |
| G2 | Symbol for gap 2. (05 Mar 2000) |
| g2 phase | <cell biology, molecular biology> The period during interphase in the cell cycle between the S phase (when DNA is replicated) and mitosis (when the nucleus, then cell, divides). at this time, the cell checks the accuracy of DNA replication and prepares for mitosis. The G stands for gap. (09 Oct 1997) |