Fig. 1. Schemata of the mitochondrial electron transport chain, showing complexes I-V, coenzyme Q and cytochrome c. Small arrows trace the flow of electrons from NADH and FADH₂ to oxygen. Large arrows show the extrusion of protons (H⁺) by complexes I, III and IV and the return of protons to the matrix via complex V, triggering the assembly of ATP (dashed arrow). Red stars indicate the two major sites of reactive oxygen formation. Uncouplers of oxidative phosphorylation allow electrons to return to the matrix without passing through complex V (after Blackstone and Kirkwood, 2003).