elektronitransportin

Elektronitransportin, commonly known as the electron transport chain, is a series of membrane-bound protein complexes and other carriers that transfer electrons from donors such as NADH and FADH2 to oxygen in aerobic organisms. The chain is embedded in the inner mitochondrial membrane of eukaryotes and in the plasma membrane of many prokaryotes, with variations among species. Its main purpose is to harvest energy from electron transfers to drive the production of ATP.

Electrons flow through a defined sequence of complexes and carriers: Complex I (NADH dehydrogenase) or Complex II (succinate dehydrogenase) feed electrons into ubiquinone (coenzyme Q), which transfers them to Complex III (cytochrome bc1), then to cytochrome c, and finally to Complex IV (cytochrome c oxidase). As electrons move through these components, protons are pumped across the membrane, creating a proton motive force. ATP synthase (often called Complex V) uses this gradient to phosphorylate ADP to ATP. Oxygen serves as the final electron acceptor at Complex IV, forming water.

The process is tightly regulated and tightly coupled to oxidative phosphorylation. In addition to mitochondria, bacteria utilize analogous chains with variations in complexes and terminal oxidases. Disruptions to electron transport can arise from genetic defects, toxins, or hypoxic conditions, and byproducts such as reactive oxygen species can be generated during imperfect electron flow. The electron transport chain is a fundamental source of cellular energy and a key target in medicine and bioenergetics research.