Figure 1.

Mitochondrial energy metabolism. Fatty acid β-oxidation and the TCA cycle produce NADH and FADH₂, which are oxidized by complexes I and II, respectively, of the electron transport chain. Electrons are transferred through the chain to the final acceptor, O₂. The free energy from electron transfer is used to pump H⁺ out of the mitochondria and generate an electrochemical gradient, Δμ_H+, across the inner mitochondrial membrane. This gradient is the driving force for ATP synthesis via the ATP synthase.