A Comparison of ATP Generation by Chemiosmosis in the Mitochondrion and Chloroplast

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OXIDATIVE PHOSPHORYLATION couples the release of energy by the oxidation of molecules derived from carbohydrates and fats to the synthesis of ATP. In cells with nuclei oxidative phosphorylation takes place only in mitochondria. The basic events of the mitochondrial process are depicted here as they are interpreted in the chemiosmotic theory. Electrons and protons (or hydrogen atoms) from carbohydrates and fats are conveyed by molecules of the hydrogen carrier NADH to a system of enzymes in the mitochondrial membrane. In respiration pairs of electrons cross the membrane three times, each time transporting two protons from inside the mitochondrion to outside. The result is a gradient in proton concentration and electric potential that tends to force the protons back through the membrane. The energy of the gradient drives the process of ATP synthesis. For each two protons traversing the F₁-F₀ complex one molecule of ATP is formed from adenosine diphosphate (ADP) and inorganic phosphate (P_i).