| one-carbon fragment | The formyl group or the methyl group that takes part in transformylation or transmethylation reactions; by means of these reactions, a group containing a single carbon atom is added to a compound being biosynthesised, adding a methyl group (as in thymidine formation), adding a hydroxymethyl group (as in serine biosynthesis), or closing a ring (as in purine formation). (05 Mar 2000) |
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| one-carbon group transferases | <enzyme> A subclass of transferases that transfer chemical groups containing a single carbon. These include the methyltransferases, the hydroxymethyl and formyl transferases, the carboxyl and carbamoyl transferases, and the amidinotransferases. Registry number: EC 2.1 (12 Dec 1998) |
| two-carbon fragment | The acetyl group (CH3CO-) that takes part in transacetylation reactions with coenzyme A as carrier; commonly referred to as acetate or acetic acid, from which it is derived. (05 Mar 2000) |
| anovulatory cycle | A sexual cycle in which no ovum is discharged. (05 Mar 2000) |
| Born-Haber cycle | <physics> This is a mathematical description of the relationship between the electron affinity, heats of atomisation, ionisation energy and lattice energy of ionic compounds. (09 Oct 1997) |
| bottoming cycle | A cogeneration system in which steam is used first for process heat and then for electric power production. (05 Dec 1998) |
| brain wave cycle | The complete upward and downward excursion of a single wave, complex, or impulse as seen on an electroencephalogram. (05 Mar 2000) |
| c3 cycle | <biochemistry> The part of the photosynthesis process where carbon dioxide is converted into three-carbon compounds, which can then be turned into six-carbon sugars. (07 Nov 1997) |
| c4 cycle | <plant biology> An alternative, very efficient pathway used by plants living in areas with low levels of carbon dioxide, to convert carbon dioxide into a form usable by the plants during photosynthesis. (09 Oct 1997) |
| Calvin Benson cycle | <biochemistry, plant biology> Metabolic pathway responsible for photosynthetic carbon dioxide fixation in plants and bacteria. The enzyme that fixes carbon dioxide is RuDP carboxylase. The cycle is the only photosynthetic pathway in C3 plants and the secondary pathway in C4 plants. The enzymes of the pathway are present in the stroma of the chloroplast. (18 Nov 1997) |
| calvin cycle | In plants, a cyclical series of carbon-fixing, sugar-producing reactions in the chloroplasts. Some of the sugars (triose phosphates) are recycled, others are stored as carbohydrates. Light is not needed for these reactions, they use the carbon dioxide and energy produced in the light reactions of photosynthesis. (09 Oct 1997) |
| cardiac cycle | The complete round of cardiac systole and diastole with the intervals between, or commencing with, any event in the heart's action to the moment when that same event is repeated. (05 Mar 2000) |
| gamma-glutamyl cycle | A proposed pathway for the glutathione-dependent transport of certain amino acids (most notably l-cystine, l-methionine, and l-glutamine) and dipeptides into certain cells; this cycle requires the formation of gamma-glutamyl amino acids and gamma-glutamyl dipeptides as well as a protein for the translocation of these di-and triisopeptides into the cells. (05 Mar 2000) |
| genesial cycle | The reproductive period of a woman's life. (05 Mar 2000) |
| visual cycle | The transformation of carotenoids involved in the bleaching and regeneration of the visual pigment. (05 Mar 2000) |