Electron carriers and energy conservation in mitochondrial respiration

The chemical system for the transformation of energy in eukaryotic mitochondria has engaged researchers for almost a century. This summary of four lectures on the electron transport system in mitochondria is an introduction to the mammalian electron transport chain for those unfamiliar with mitochondrial oxidative phosphorylation. It gives references chosen to reflect the history of the field and to highlight some of the recent advances in bioenergetics. The electron transport chain converts the energy that is released as electrons are passed to carriers of progressively higher redox potential into a proton gradient across the membrane that drives adenosine triphosphate (ATP) synthesis. The electron carriers include flavins, iron–sulfur centers, heme groups, and copper to divide the redox change from reduced nicotinamide adenine dinucleotide (NADH) at −320 mV to oxygen at +800 mV into steps that allow conversion and conservation of the energy released in three major complexes (Complexes I, III, and IV) by moving protons across the mitochondrial inner membrane. The three processes of proton pumping are now known after the successful determination of the structures of the large membrane protein complexes involved. Mitochondria and their proteins play roles not only in the production of ATP but also in cell survival, for which energy supply is the key.