piielektronijärjestelmä

The piielektronijärjestelmä, often translated as the "electron transport chain" or "electron transfer system," is a series of protein complexes and mobile electron carriers embedded in the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes. Its primary function is to facilitate the controlled release of energy from the oxidation of nutrients, such as glucose, and to transfer this energy into a usable form for the cell, primarily adenosine triphosphate (ATP).

The process begins with the transfer of high-energy electrons from electron carriers like NADH and FADH2 to the first complex in the chain. As these electrons move through a series of redox reactions from one carrier to the next, they release energy. This released energy is used by some of the protein complexes to pump protons (H+) from the mitochondrial matrix (or cytoplasm in prokaryotes) across the inner membrane into the intermembrane space (or periplasmic space). This creates an electrochemical gradient, also known as the proton-motive force.

The final electron acceptor in aerobic respiration is oxygen, which combines with electrons and protons to form water. The accumulated proton gradient then drives the synthesis of ATP through a process called chemiosmosis, where protons flow back across the membrane through an enzyme called ATP synthase. This intricate system is fundamental to cellular respiration and energy production in most living organisms.