Kemiosmoosia

Kemiosmoosia is a biological process that describes the movement of ions across a selectively permeable membrane down their electrochemical gradient. This movement is coupled to the synthesis of ATP, the primary energy currency of cells. The term "chemiosmosis" was coined by Peter Mitchell in 1961, who proposed this mechanism as the main way cells generate ATP during cellular respiration and photosynthesis.

The process relies on the establishment of a proton gradient across a membrane, typically the inner mitochondrial membrane or the thylakoid membrane of chloroplasts. This gradient is created by a series of electron transport chains that pump protons from one side of the membrane to the other, using energy derived from the oxidation of fuel molecules or light. The accumulation of protons on one side of the membrane creates both a concentration difference and an electrical potential difference, collectively known as the proton-motive force.

Protons then flow back across the membrane through a specialized enzyme complex called ATP synthase. As protons pass through ATP synthase, they drive the synthesis of ATP from ADP and inorganic phosphate. This proton flow is an exergonic process, and the energy released is harnessed by ATP synthase to form the high-energy phosphate bond in ATP. Kemiosmoosia is thus a fundamental mechanism for energy conversion in living organisms.