Summary: Pyruvate is degraded and combined with Coenzyme-A to form acetyl coenzyme A; hydrogens are released; and carbon dioxide is released. The pyruvic molecules formed in glycolosis enter the mitochondria, where they are converted to acetyl Coenzyme-A (acetyl-CoA). In this complex series of reactions, pyruvate undergoes oxidative decarboxylation. First, a carboxyl group is removed as carbon dioxide, which diffuses out of the cell. Then the two-carbon fragment remaining is oxidized, and the hydrogens that were removed during the oxidation are accepted by NAD+. Finally, the oxidized two-carbon fragment, an acetyl group, is attached to Coenzyme-A, which is manufactured in the cell from one of the B vitamins, pantothenic acid. The reaction is catalyzed by a multienzyme complex that contains several copies of each of three different

enzymes. The overall reaction for the formation of acetyl Coenzyme-A can be stated as follows: 2 pyruvate + 2 NAD+ + 2 CoA ----> 2 acetyl-CoA + 2 NADH + 2 carbon dioxide Note that the original glucose molecule has now been oxidized to two acetyl groups and two carbon dioxide molecules. The hydrogens removed have reduced NAD+ to NADH. At this point in aerobic respiration, four NADH molecules have been formed from a single starting glucose molecule, two during glycolosis and two during the formation of acetyl-CoA from pyruvate.