A schematic illustration of the basic structural and functional aspects of the mitochondrion.

Mitochondrial genome contributes polypeptide subunits to the five enzyme complexes that comprise the oxidative phosphorylation (OXPHOS) system within the inner mitochondrial membrane, the site of ATP synthesis. The reoxidation of reducing equivalents, NADH (reduced nicotinamide adenine dinucleotide) and FADH₂ (reduced flavin adenine dinucleotide), that are produced by the oxidation of carbohydrates (the tricarboxylic acid (TCA) cycle) and fatty acids is coupled to the generation of an electrochemical gradient across the inner mitochondrial membrane, which is harnessed by the ATP synthase to drive the formation of ATP.