citric acid cycle

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citric acid cycle

A Dictionary of Plant Sciences | 1998 | | © A Dictionary of Plant Sciences 1998, originally published by Oxford University Press 1998. (Hide copyright information) Copyright

citric acid cycle (Krebs' cycle, tricarboxylic acid cycle) The cyclic series of reactions which represent the principal means by which most living cells provide hydrogen and electrons for the generation of ATP via the electron-transport chain and oxidative phosphorylation. The hydrogen is taken up by NAD (nicotinamide adenine dinucleotide) or FAD (flavin adenine dinucleotide) and passed into the electron-transport chain. The reactions result in oxidative decarboxylation. The sequence is initiated when acetyl groups, fed in by acetyl coenzyme A, are dehydrogenated (i.e. oxidized), to release 4 pairs of hydrogen atoms, and decarboxylated to form 2 molecules of carbon dioxide. This yields oxaloacetic acid and then citric acid. The citric acid passes through a series of reactions wherein oxaloacetic acid is reformed, and two moles of CO2 and water and one mole of ATP are synthesized. Since two molecules of acetyl coenzyme A are formed for each glucose molecule that is oxidized the cycle rotates twice, forming two moles of ATP.

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MICHAEL ALLABY. "citric acid cycle." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. 22 Nov. 2009 <http://www.encyclopedia.com>.

MICHAEL ALLABY. "citric acid cycle." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. (November 22, 2009). http://www.encyclopedia.com/doc/1O7-citricacidcycle.html

MICHAEL ALLABY. "citric acid cycle." A Dictionary of Plant Sciences. 1998. Retrieved November 22, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O7-citricacidcycle.html

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citric-acid cycle

A Dictionary of Biology | 2004 | © A Dictionary of Biology 2004, originally published by Oxford University Press 2004. (Hide copyright information) Copyright

citric-acid cycle See Krebs cycle.

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citric-acid cycle

A Dictionary of Zoology | 1999 | | © A Dictionary of Zoology 1999, originally published by Oxford University Press 1999. (Hide copyright information) Copyright

citric-acid cycle (Krebs's cycle, tricarboxylic-acid cycle) A cyclic series of reactions which take place in mitochondria, in the presence of oxygen. The cycle represents the principal means by which most living cells provide electrons for the generation of ATP via the electron-transport chain and oxidative phosphorylation. The sequence is initiated by the condensation of acetyl coenzyme A with oxaloacetic acid to form citric acid. This then passes through a series of reactions wherein oxaloacetic acid is reformed, and 2 moles of CO2 and water and 12 moles of ATP are synthesized.

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MICHAEL ALLABY. "citric-acid cycle." A Dictionary of Zoology. 1999. Retrieved November 22, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-citricacidcycle.html

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