Figure 1. Mitochondrial energy metabolism and the respiratory chain.

Acetyl-coenzyme A (Acetyl-CoA) is the terminal product of carbohydrate and lipid metabolism, and is oxidized through the reactions of the Krebs cycle to produce CO₂. The high energy electrons (e⁻) produced by these reactions enter the respiratory chain and eventually reduce molecular oxygen (0₂) to form water (H₂0). The energy released by this process is used to pump protons (H⁺) across the mitochondrial inner membrane and generate the electrochemical gradient that enables complex V to synthesize ATP. The red ovals represent mitochondrial DNA-encoded subunits of the respiratory chain complexes. CoQ, coenzyme Q.