Figure 1.

Mitochondrial oxidative phosphorylation (OXPHOS). A mitochondrion is comprised of an outer mitochondrial membrane (OMM), intermembrane space (IMS), inner mitochondrial membrane (IMM) and matrix. Electrons from NADH and FADH₂ enter the electron transport chain (ETC) at complex I (CI) and complex II (CII), respectively, and are passed to ubiquinone (Q), which then transfers electrons to complex III (CIII). Cytochrome c (Cyt C) transfers electrons from CIII to complex IV (CIV) where O₂ as the final electron acceptor is reduced to H₂O. The movement of electrons along the electron transport chain (ETC) results in protons (H⁺) being pump out from the matrix to the IMS at CI, CIII, and CIV. Ultimately, protons are channeled back into the matrix through complex V (CV) where ADP and P are coupled to form ATP.