Figure 1 Oxidative phosphorylation Figure 1 | Oxidative phosphorylation. The respiratory chain and oxidative phosphorylation system are embedded in the inner mitochondrial membrane and represent the major site of ATP production within the cell. Transfer of electrons derived from NADH and reduced flavin adenine dinucleotide (FADH2) is coupled to proton pumping to generate an electrochemical gradient across the inner mitochondrial membrane. This electrochemical gradient is harnessed by ATP synthase to drive the synthesis of ATP from ADP and inorganic phosphate (Pi). Five different protein complexes are involved: NADH-ubiquinone oxidoreductase (complex I), succinate ubiquinone oxidoreductase (complex II), ubiquinone cytochrome c oxidoreductase (complex III), cytochrome c oxidase (complex IV) and ATP synthase (complex V), in addition to two mobile electron carriers: coenzyme Q10 (Q) and cytochrome c (Cyt c). e-, electron. Chow, J. et al. (2016) Mitochondrial disease and endocrine dysfunction Nat. Rev. Endocrinol. doi:10.1038/nrendo.2016.151