At the end of glycolysis, 2 molecules of pyruvic acid are formed in the cytoplasm. The 2 molecules of pyruvic acid enters mitochondria to undergo oxidative decarboxylation to form acetyl fraction (2C) in the presence of enzyme pyruvate dehydrogenase and Mg2+ as co-factor. 2 molecules of acetyl fraction (2C) combine with 2 molecules of coenzyme A to form 2 molecules of acetyl coenzyme A (2C). The two molecules of hydrogen released during this reaction are accepted by 2 molecules of coenzyme NAD+ and it is reduced to form 2 molecules of NADH + H+.