| glycine-succinate 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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| restored cycle | An atrial or ventricular cardiac cycle that follows the returning cycle and resumes the normal rhythm. (05 Mar 2000) |
| glyoxylate cycle | <biochemistry> Metabolic pathway present in bacteria and in the glyoxisome of plants, in which two acetyl CoA molecules are converted to a 4 carbon dicarboxylic acid, initially succinate. Includes two enzymes not found elsewhere, isocitrate lyase and malate synthase. Permits net synthesis of carbohydrates from lipid and hence is prominent in those seeds in which lipid is the principal food reserve. (18 Nov 1997) |
| glyoxylic acid cycle | A catabolic cycle in plants and microorganisms like that of the tricarboxylic acid cycle in animals; its key reaction is the condensation of acetyl-CoA with glyoxylic acid to malic acid (analogous to the condensation of acetyl-CoA and oxaloacetic acid to form citric acid in the tricarboxylic acid cycle). Synonym: Krebs-Kornberg cycle. (05 Mar 2000) |
| pentose phosphate cycle | <biochemistry> A pathway of hexose oxidation in which glucose-6-phosphate undergoes two successive oxidations by NADP, the final one being an oxidative decarboxylation to form a pentose phosphate. Diverges from this when glucose-6-phosphate is oxidized to ribose 5 phosphate by the enzyme glucose-6 phosphate dehydrogenase. This step reduces NADP to NADPH, generating a source of reducing power in cells for use in reductive biosyntheses. In plants, part of the pathway functions in the formation of hexoses from carbon dioxide in photosynthesis. Also important as source of pentoses, for example for nucleic acid biosynthesis. This pathway is the main metabolic pathway in neutrophils, congenital deficiency in the pathway produces sensitivity to infection. Alternative metabolic route to Embden Meyerhof pathway for breakdown of glucose. (18 Nov 1997) |
| gonadotrophic cycle | One complete round of ovarian development in the insect vector from the time when the blood meal is taken to the time when the fully developed eggs are laid. (05 Mar 2000) |
| returning cycle | An atrial or ventricular cardiac cycle that begins with an extrasystole or a forced beat. (05 Mar 2000) |
| menstrual cycle | The reproductive cycle of female humans. The cycle is characterised by a monthly discharge of blood, mucus, and tissues from the uterus (called menstruation) and involves changes to the lining of the uterus (the endometrium) during the rest of the month including a few days of fertility after an ovum (egg) is released by an ovary. (09 Oct 1997) |
| chewing cycle | A complete course of movement of the mandible during a single masticatory stroke. (05 Mar 2000) |
| Ross cycle | The life cycle of the malaria parasite. (05 Mar 2000) |
| citric 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) |
| mitotic cycle | <cell biology, molecular biology> The sequence of events between mitotic divisions. The cycle is conventionally divided into G0, G1, (G standing for gap), S (synthesis phase during which the DNA is replicated), G2 and M (mitosis). Cells that will not divide again are considered to be in G0 and the transition from G0 to G1 is thought to commit the cell to completing the cycle and dividing. (26 Mar 1998) |
| combined cycle | Two or more generation processes in series or in parallel, configured to optimise the energy output of the system. (05 Dec 1998) |
| combined-cycle power plant | The combination of a gas turbine and a steam turbine in an electric generation plant. The waste heat from the gas turbine provides the heat energy for the steam turbine. (05 Dec 1998) |
| Cori cycle | The phases in the metabolism of carbohydrate: 1) glycogenolysis in the liver; 2) passage of glucose into the circulation; 3) deposition of glucose in the muscles as glycogen; 4) glycogenolysis during muscular activity and conversion to lactate, which is converted to glycogen in the liver. (05 Mar 2000) |