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tri·car·box·yl·ic ac·id cy·cle
tri·car·box·yl·ic ac·id cy·cle(TCA cycle) (trī-kahr-bok-sil'ik as'id sī'kĕl)
Synonym(s): Krebs cycle.
Krebs cycleA cyclical sequence of 10 biochemical reactions, brought about by mitochondrial enzymes, that involves the oxidation of a molecule of acetyl-CoA, to two molecules of carbon dioxide and water. Each turn of the cycle can result in the formation of 12 molecules of ATP per molecule of acetyl-CoA. ATP is the direct source of energy for all work performed in any cell. The Krebs cycle is one of the most important in all body biochemistry and occurs in all organisms that oxidise food totally to carbon dioxide and water. Also known as the citric acid cycle or the tricarboxylic acid cycle. (Hans Adolf Krebs, 1900–89, German-born English biochemist)
Krebs cycle or tricarboxylic acid cycle (TCA cycle) or (formerly) citric-acid cyclea circular series of reactions that forms part of CELL RESPIRATION in the presence of oxygen, occurring in many microorganisms as well as higher organisms. In eukaryotes the cycle occurs in the matrix of MITOCHONDRIA. The steps of the cycle were deduced by Sir Hans Krebs (1900–81), for which he received a Nobel Prize. The reactions leading up to the cycle by which ACETYLCOENZYME A is produced, together with the overall role of the cycle in the breakdown of complex molecules is described fully under AEROBIC RESPIRATION.
Each turn of the cycle releases 2 molecules of carbon dioxide, 8 hydrogen atoms that produce 11 molecules of ATP via the ELECTRON TRANSPORT SYSTEM, and 1 molecule of ATP produced by SUBSTRATE-LEVEL PHOSPHORYLATION. Two turns of the cycle are needed to complete the breakdown of one glucose molecule.
Krebs,Sir Hans Adolph, German biochemist in England and Nobel laureate, 1900-1981.
Krebs cyclea sequence of reactions within mitochondria, constituting the final common pathway for the oxidation of all fuel molecules (glucose, fatty acids and amino acids), in which carbon atoms enter the cycle as acetyl-CoA and emerge as carbon dioxide, and the electrons produced are transferred to the electron transport chain. Also provides intermediates for biosynthetic processes. Syn citrate cycle, citric acid cycle, tricarboxylic cycle.
|Table C9 Relationship between the minimum angle of resolution, the Snellen fraction and the equivalent spatial frequency of a sine wave|
|resolution (min of |
|(m)||(ft)||Spatial frequency (cpd)|