Mechanism of Mitochondrial Electron Transport and Proton Pumping
The light purple band is the inner mitochondrial membrane. The dark purple ovals are protein complexes. DH is the NADH dehydrogenase. Cyt is the cytochrome b-c1 complex. Oxid is the cytochrome oxidase complex. The small unlabeled peripheral protein is cytochrome c. The mobile cofactor is ubiquinone/ubihydroquinone. Study the animation by following the electrons as they move through the electron transport chain starting from NADH and ending in water molecules. Also note that as the electrons move through the electron transport chain, protons are taken up on the matrix side of the membrane and they are released into the intermembrane space on the other side of the membrane. As the electron transport chain operates, an electrochemical gradient of protons develops across the membrane. This electrochemical gradient has the energy needed to drive the synthesis of ATP at coupling factor. You can click on the animation above to see a larger version. For a more detailed look at the mechanism by which quinones can mediate proton pumping, see the animation of plastoquinone mediated proton uptake. Ubiquinone mediated proton pumping in the mitochondria is very similar to plastoquinone mediated proton pumping in the thylakoid membrane.