The pyruvic acid formed during glycolysis enters to mitochondria where oxidative Decarboxylation takes place and acetyl Co-A is formed. It occurs in presence of NAD⁺, pyruvic acid Dehydrogenase complex and coenzyme-A. pyruvic acid + NAD⁺ $\rightarrow$ Acetyl Co-A + NADH + H⁺ + C$O_{2}$