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Pyruvic acid is first decarboxylated (release of CO₂) and then oxidized by a molecule of NAD⁺ (reduced to NADH + H⁺) to form the two carbon molecules of acetyl‐CoA. As two molecules of pyruvic acid are produced from a glucose molecule, two molecules of CO₂, NADH + H⁺, and acetyl‐CoA are produced. In prokaryotic cells (e.g. bacteria), the citric acid cycle (or Krebs cycle) occurs in the cytosol, while in eukaryotic organisms (e.g. yeast), it takes place in the mitochondrial matrix.

Overall, two molecules of CO₂ are produced and three molecules of NAD⁺ are reduced to NADH + H⁺ during a turn of the citric acid cycle. Besides, two electrons and two protons released from pyruvic acid are used to reduce a molecule of flavin adenine dinucleotide (FAD) into FADH₂, similar to that of NAD⁺. Finally, there is a release of chemical energy, which allows the synthesis of an ATP molecule. To summarize, for each molecule of glucose oxidized, four molecules of CO₂, six molecules of NADH + H⁺, two molecules of FADH₂, and two molecules of ATP are generated.