Figure 1.

Overview of mitochondrial metabolism. Mitochondria contain an outer and inner membrane. The mitochondrial matrix enclosed by the inner membrane contains the TCA cycle that generates reducing equivalents NADH and FADH₂, which donate electrons to the electron transport chain (ETC), resulting in the generation of a proton motive force to drive ATP synthesis. The ETC is composed of two supercomplexes consisting of either complex I–III–IV or II–III–IV. (Modified from http://en.wikipedia.org/wiki/Electron_transport_chain#mediaviewer/File:Mitochondrial_electron_transport_chain%E2%80%94Etc4.svg.)