ElektronentransportSystem

ElektronentransportSystem is a term used in biochemistry and physiology to describe a series of membrane-bound protein complexes and mobile carriers that transfer electrons through redox reactions, ultimately converting energy stored in reducing equivalents into a transmembrane proton gradient. The flow of electrons is coupled to the translocation of protons across a membrane, and the resulting proton motive force drives ATP synthesis via ATP synthase. In aerobic respiration, oxygen serves as the terminal electron acceptor, producing water; in some anaerobic organisms, other acceptors such as nitrate or sulfate are used.

In eukaryotes, the system is located in the inner mitochondrial membrane. The main components are Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), ubiquinone (coenzyme Q), Complex III (cytochrome bc1 complex), cytochrome c, and Complex IV (cytochrome c oxidase). Electrons entering at Complex I from NADH travel through ubiquinone and Complex III to cytochrome c and Complex IV, while electrons from FADH2 enter at Complex II. Complexes I, III, and IV pump protons to generate the electrochemical gradient; ATP synthase uses this gradient to synthesize ATP. The exact ATP yield per glucose varies with organism and conditions.

In bacteria and archaea, the electron transport system can be organized in branched networks and may utilize different terminal electron acceptors. In photosynthetic organisms, light-driven electron transport chains in chloroplasts or bacterial membranes power ATP production and reducing power for carbon fixation. The ElektronentransportSystem is central to energy metabolism, and defects in its components can contribute to metabolic or mitochondrial disorders.