What are the three major steps in mitochondrial oxidative phosphorylation?

Mitochondrial oxidative phosphorylation is the final step in cellular respiration, following glycolysis, pyruvate oxidation, and the citric acid cycle. Using the electron transport chain and ATP synthase, which are embedded in the inner mitochondrial membrane, the process produces ATP.

The first step in oxidative phosphorylation is the oxidation, or loss of electrons, from NADH and FADH₂, two of the products from the citric acid cycle. Second, the oxidation of NADH creates a proton gradient across the inner mitochondrial membrane, from pumping protons through the protein complexes of the electron transport chain, from the matrix into the intermembrane space. Meanwhile, oxygen is reduced in the matrix, accepting electrons and combining with protons to produce water. Finally, electrons flow down the resulting protein gradient through ATP synthase, which produces ATP from ADP.