How does oxidative phosphorylation produce ATP?

Oxidative phosphorylation requires the electron carrier system; comprised of four protein complexes (complexes I - IV) as well as the enzyme ATPase. These are intrinsic enzymes that line the inner mitochondrial membrane. Coenzymes NAD and FAD are reduced by the oxidation of intermediates within the Krebs cycle. The reduced coenzymes diffuse to the internal mitochondrial membrane and have the ability to reduce the complexes in the electron carrier system. Reduced NAD reduces complex I by donating an electron; reduced FAD reduces complex II. In doing this, energy is released which actively transport one proton into the inter-membrane space, against its concentraiton gradient. This maintains a high proton gradient within the inter-membrane space, allowing the protons to diffuse back into the mitochondrial matrix passively. When one proton diffuses back into the matrix, it drives the enzyme ATPase within the inner membrane. This catalyses the conversion of one ADP + Pi molecule to one ATP molecule.Reduced complex I reduces complex II, and so on, until the electron reaches complex IV. When it reaches complex IV, it reduces oxygen to water. Reduced NAD reduces complex I, so the electron (the reducing agent) can reduce three proteins in the electron carrier system and hence drive three protons into the inner mitochondrial membrane. As 10 NAD coenzymes are reduced for each glucose molecules, 30 ATP molecules can be synthesised via reduced NAD. Reduced FAD reduces complex II, so the electron can reduce two proteins in the electron carrier system and hence drive two protons into the inner mitochondrial membrane. As 2 FAD coenzymes are reduced for each glucose molecule, 4 ATP molecules can be synthesised via reduced FAD.