Figure 1

Mitochondrial respiratory chain complexes. Respiratory chain complexes I–IV generate a proton gradient on the mitochondrial inner membrane that facilitates ATP production by complex V (ATP synthase). The electron (e−) passes through complex I and complex II, respectively, and moves to complex III via the CoQ. Cytochrome c (Cyt c) transfers an electron from complex III to complex IV, which reduces O2 to form H2O. Electron flow involves proton (H+) transfer across the mitochondrial inner membrane at complexes I, III, and IV, creating an electrochemical gradient. Complex V uses the proton motive force to generate ATP.