The citric acid cycle (TCA) is a series of oxidation-reduction reactions that harvests energy from acetyl groups and fully oxidizes them to carbon dioxide. It occurs in mitochondria and involves 8 steps where acetyl-CoA condenses with oxaloacetate to form citrate, followed by isomerization and oxidative decarboxylations to generate NADH and FADH2. One turn of the cycle fully oxidizes two carbons of acetyl-CoA to CO2 while capturing energy as electrons to power ATP synthesis. The cycle is regulated by substrate availability and product inhibition at key irreversible steps to optimize energy production.