The citric acid cycle, also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle, is a series of
chemical reactions to release stored energy through the
oxidation of
acetyl-CoA derived from
carbohydrates,
fats, and
proteins. In addition, the cycle provides
precursors of certain
amino acids, as well as
NADH, a
reducing agent, which are used in numerous other reactions. Its central importance to many
biochemical pathways suggests that it was one of the earliest components of
metabolism and may have originated
abiogenically. The German-born British biochemist
Hans Krebs received the 1953
Nobel Prize in Physiology or Medicine for his identification of the cycle in 1937. The name of this metabolic pathway is derived from
citric acid, which is consumed and then regenerated by this sequence of reactions to complete the cycle. The cycle consumes acetate (in the form of
acetyl-CoA) and
water, and reduces NAD+ to NADH, releasing carbon dioxide. The NADH generated by the cycle is fed into the
oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of
nutrients to produce usable chemical energy in the form of
adenosine triphosphate. These processes are depicted in this overview diagram of the citric acid cycle.Diagram credit:
YassineMrabet; edited by
Narayanese and
TotoBaggins; vectorized by
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