In Mitochondria, the pyruvic acid is broken down into carbon dioxide, water and energy. Pyruvic oxidation: A carboxyl group is removed from pyruvate and released as carbon dioxide. The two carbon molecule from the first step is oxidized, and NAD+ accepts the electrons to form NADH. The oxidized two-carbon molecule, an acetyl group, is attached to Coenzyme A to form acetyl CoA.