Elektrontransportjärjestelmällä

Elektrontransportjärjestelmällä, often referred to as the electron transport chain or ETC, is a crucial series of protein complexes embedded in the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes. Its primary function is to facilitate the controlled transfer of electrons from electron donor molecules, such as NADH and FADH2, to a final electron acceptor, typically oxygen. This stepwise electron transfer releases energy, which is then harnessed to pump protons across the membrane, establishing an electrochemical gradient.

The electron transport chain consists of several distinct complexes, including Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), Complex III (cytochrome c reductase), and Complex IV (cytochrome c oxidase). Each complex catalyzes specific redox reactions, passing electrons along a sequence of carriers like cytochromes and iron-sulfur proteins. As electrons move from higher to lower energy levels, energy is released and used by proton pumps within Complexes I, III, and IV to translocate protons from the mitochondrial matrix to the intermembrane space.

The resulting proton gradient, also known as the proton-motive force, represents stored potential energy. This energy is subsequently utilized by ATP synthase, an enzyme that couples the flow of protons back into the matrix with the synthesis of adenosine triphosphate (ATP), the main energy currency of the cell. This process, known as oxidative phosphorylation, generates the vast majority of ATP produced during aerobic respiration. The electron transport chain is therefore indispensable for life, providing the energy required for numerous cellular activities.