In aerobic respiration, pyruvic acid is transported to mitochondria from cytosol. Each pyruvic acid is oxidized to carbon dioxide in a reaction called oxidative decarboxylation, that is, pyruvate is first decarboxylation an then oxidized by the enzyme pyruvate dehydrogenase. The combination of the remaining 2—carbon acetate unit is readily accepted by coenzyme A (CoA), to form Acety-CoA. During this process, 2 molecules of NADH are produced. Now acetyl CoA enters into citric acid cycle. One molecule of acetyl —CoA combines with oxalo acetic acid (AOO) (4C) to form 6 carbon citric acid and CoA is released.
This reaction take place in the presence of citrate synthase, citrate is then isomerised to isocitrate. It is followed by two successive steps of decarboxylation, leading to the formation of a ketogutaric acid and succinyl CoA. In the remaining step of TCA, succinyl CoA is oxidized to OAA (Oxalo Acotic Acid), allowing the cycle Continue. During this cycle 3 molecules of NAD+ and one molecule of FDA are reduced to produce NADH and FADH2 respectively. One molecule of GTP is also produced.