<P> The citric acid cycle (CAC)--also known as the tricarboxylic acid (TCA) cycle or the Krebs cycle--is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl - CoA derived from carbohydrates, fats, and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP). In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other biochemical reactions . Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically . </P> <P> The name of this metabolic pathway is derived from the citric acid (a type of tricarboxylic acid, often called citrate, as the ionized form predominates at biological pH) that 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, reduces NAD to NADH, and produces carbon dioxide as a waste byproduct . The NADH generated by the citric acid 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 ATP . </P>

In what part of the mitochondria does krebs cycle occur