Pyruvate, which is produced in the cytosol through glycolysis, is oxidized within the mitochondria where it provides a source of energy in the citric acid cycle and increases oxidative phosphorylation. Pyruvate oxidation converts pyruvate (a 3 carbon molecule) via pyruvate dehydrogenase into acetyl-CoA. This produces an NADH molecule and a carbon dioxide molecule as by-products. The acetyl-CoA molecule functions as a source of energy to drive the citric acid cycle during cellular respiration.