Hapetinjohtojärjestelmän

Hapetinjohtojärjestelmän, often translated as the oxidative phosphorylation system, is a metabolic pathway that occurs in the mitochondria of eukaryotic cells. This intricate process is the primary mechanism by which cells generate adenosine triphosphate (ATP), the main energy currency of the cell. It involves a series of protein complexes embedded within the inner mitochondrial membrane.

The system begins with the transfer of electrons from electron carriers, primarily NADH and FADH2, which are produced during earlier stages of cellular respiration like glycolysis and the Krebs cycle. These electrons are passed along a chain of protein complexes, releasing energy at each step. This released energy is used to pump protons (H+ ions) from the mitochondrial matrix across the inner membrane into the intermembrane space.

This proton pumping creates an electrochemical gradient, often referred to as the proton-motive force. This force represents stored potential energy. The protons then flow back into the mitochondrial matrix down their concentration gradient through a special enzyme called ATP synthase. This flow of protons drives the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi).

Oxygen acts as the final electron acceptor in the electron transport chain. It combines with electrons and protons to form water. Without oxygen, the electron transport chain would halt, and ATP production through oxidative phosphorylation would cease, leading to cell death. The efficiency of hapetinjohtojärjestelmän in ATP production is significantly higher compared to anaerobic respiration.