Elektrontransportjärjestelmä

Elektrontransportjärjestelmä, often referred to as the electron transport chain, is a series of protein complexes and other molecules embedded in the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes. Its primary function is to generate adenosine triphosphate (ATP), the main energy currency of the cell, through a process called oxidative phosphorylation.

The system operates by accepting high-energy electrons from electron carriers, specifically NADH and FADH2, which are produced during earlier stages of cellular respiration like glycolysis and the Krebs cycle. These electrons are then passed sequentially from one complex to another. As electrons move through the chain, they release energy. This released energy is used by some of the protein complexes to pump protons (H+ ions) from the mitochondrial matrix (or cytoplasm in prokaryotes) into the intermembrane space (or periplasmic space).

This proton pumping creates an electrochemical gradient across the membrane, with a higher concentration of protons in the intermembrane space. This gradient represents stored potential energy, similar to water behind a dam. Protons then flow back down their concentration gradient through a specialized enzyme called ATP synthase. The flow of protons through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate.

Oxygen serves as the final electron acceptor in aerobic respiration. At the end of the electron transport chain, electrons combine with oxygen and protons to form water. Without oxygen, the electron transport chain would halt, severely impairing ATP production. The efficiency of the electron transport chain in generating ATP makes it a crucial component of cellular energy metabolism.