Citric acid cycle
= Citric acid cycle
{tag=Energy metabolism}
{wiki}
= TCA cycle
{c}
{synonym}
The <citric acid cycle> is a <metabolic pathway> that accepts a two-<carbon> <acetyl group> from <acetyl-CoA>, releases two <carbon dioxide> <molecules> per turn, and regenerates its four-<carbon> acceptor, <oxaloacetate>. Its <oxidation> steps load <electron carriers>; <oxidative phosphorylation> subsequently uses their <electrons> to support <ATP> production. In <mitochondria>, most steps occur in the <mitochondrial matrix>, while <succinate dehydrogenase> lies in the <inner mitochondrial membrane>.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others/How Cells Obtain Energy from Food>[Molecular Biology of the Cell, 4th edition by Bruce Alberts and others; Chapter 2, How Cells Obtain Energy from Food, The Citric Acid Cycle Generates NADH by Oxidizing Acetyl Groups to CO2; Figure 2-79 and Panel 2-9]{ref}
The economy is striking: the acceptor is rebuilt rather than supplied anew for every incoming <acetyl group>. Regeneration does not create extra <oxaloacetate>. Withdrawal of intermediates for <amino acid> synthesis must be balanced by replenishment if the available pool is to remain steady. Thus the <citric acid cycle> connects <energy metabolism> to synthesis as well as to breakdown.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others/How Cells Obtain Energy from Food>[Molecular Biology of the Cell, 4th edition by Bruce Alberts and others; Chapter 2, How Cells Obtain Energy from Food, final paragraph of The Citric Acid Cycle Generates NADH by Oxidizing Acetyl Groups to CO2: oxaloacetate and alpha-ketoglutarate as biosynthetic precursors]{ref}