1. Conversion to Acetyl CoA: Pyruvic acid is first decarboxylated and oxidized to form acetyl-CoA. This reaction is catalyzed by the enzyme pyruvate dehydrogenase complex.
2. Citric Acid Formation: Acetyl-CoA enters the citric acid cycle by condensing with a four-carbon molecule called oxaloacetate to form a six-carbon molecule called citrate. This reaction is catalyzed by the enzyme citrate synthase.
3. Series of Oxidative Reactions: Citrate undergoes a series of oxidative reactions, including dehydrogenation and decarboxylation, leading to the production of carbon dioxide, NADH, and FADH2. These reactions are catalyzed by various enzymes, including isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and succinate dehydrogenase.
4. Regeneration of Oxaloacetate: The final step of the citric acid cycle involves the regeneration of oxaloacetate from malate. This reaction is catalyzed by the enzyme malate dehydrogenase.
Through these reactions, the pyruvic acid molecule is completely oxidized, releasing energy in the form of NADH, FADH2, and GTP. These molecules will later enter the electron transport chain to produce ATP through oxidative phosphorylation.
