| Tc | cytotoxic T-cell; the generation time of a cell cycle; tricuspid closure |
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| tG1 | the time required to complete the G1 phase of the cell cycle |
| tG2 | the time required to complete the G2 phase of the cell cycle |
| tM | the time required to complete the M phase of the cell cycle |
| tS | time required to complete the S phase of the cell cycle |
| Shemin cycle | A series of metabolic steps in which glycine is condensed with succinyl-CoA and is then oxidised to CO2 and H2O with regeneration of the succinyl-CoA; important in the synthesis of d-aminolevulinic acid and in the metabolism of red blood cells. Synonym: Shemin cycle. (05 Mar 2000) |
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| nitrogen cycle | <biochemistry> The global cycle of moving various forms of nitrogen through the air, water, soil, plants, animals of the planet. See: nitrogen fixation. (09 Oct 1997) |
| substrate cycle | <biochemistry> Any seqence of enzyme catalysed reactions in which the forward and reverse processes (catalysed by different enzymes) are consititutively active. Frequently used to describe the cycle of phosphorylation and dephosphorylation of phosphatidyl inositol derivatives in cell membranes. (05 Jan 1998) |
| succinic acid cycle | A series of oxidation reduction reactions in which succinic acid and other 4-carbon atoms acids (fumaric, malic, oxaloacetic) take part in the oxidation of pyruvic acid as part of the tricarboxylic acid cycle. See: dicarboxylic acid cycle. (05 Mar 2000) |
| dicarboxylic acid cycle | That portion of the tricarboxylic acid cycle involving the dicarboxylic acids (succinic, fumaric, malic, and oxaloacetic acids), a cyclic scheme in which certain steps of the tricarboxylic acid cycle are used with the glyoxylate cycle; important in the utilization of glyoxylic acid in microorganisms. (05 Mar 2000) |
| direct life cycle | <epidemiology> A life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species. (05 Dec 1998) |
| indirect life cycle | <epidemiology> A life cycle which requires one or more intermediate hosts before the definitive host species is reinfected. Compare direct, nondirect. (05 Dec 1998) |
| isometric period of cardiac cycle | That period in which the muscle fibres do not shorten although the cardiac muscle is excited and the pressure in the ventricles rises, extending from the closure of the atrioventricular valves to the opening of the semilunar valves (isovolumic constriction) or the reverse (isovolumic relaxation). (05 Mar 2000) |
| ornithine cycle | The metabolic pathway isfound in vertebrates and takes place in theliver, in it, urea is synthesised from amino acids and carbon dioxide. (09 Oct 1997) |
| ovarian cycle | The normal sex cycle which includes development of an ovarian (graafian) follicle, rupture of the follicle with discharge of the ovum, and formation and regression of a corpus luteum. (05 Mar 2000) |
| TCA cycle | <biochemistry> The central feaure of oxidative metabolism. Cyclic reactions whereby acetyl CoA is oxidized to carbon dioxide providing reducing equivalents (NADH or FADH2) to power the electron transport chain. Also provides intermediates for biosynthetic processes. (16 Dec 1997) |
| thermal conversion cycle | <radiobiology> Process of generating electrical power with a fusion reactor by means of a steam / other gas turbine. This is distinct from direct conversion cycles. (09 Oct 1997) |
| topping cycle | A cogeneration system in which electric power is produced first. The reject heat from power production is then used to produce useful process heat. (05 Dec 1998) |
| endogenous cycle | The portion of a parasitic life cycle occurring within the host. (05 Mar 2000) |
| tricarboxylic acid cycle | <biochemistry> The central feaure of oxidative metabolism. Cyclic reactions whereby acetyl CoA is oxidized to carbon dioxide providing reducing equivalents (NADH or FADH2) to power the electron transport chain. Also provides intermediates for biosynthetic processes. (16 Dec 1997) |