How is the electron transport chain used to generate ATP?

The four protein complexes make up the main structure of the electron transport chain. Electrons from NADH and FADH2 molecules, which are generated during the earlier steps of cellular respiration, are passed through the four protein complexes. As the electrons move through the protein complexes, protons (H+) are actively pumped across the inner mitochondrial membrane, creating a proton gradient. Protons then flow back into the mitochondrial matrix through ATP synthase, an enzyme complex present in the mitochondrial membrane. The energy released during the flow of protons through ATP synthase is harnessed and used to generate ATP, the energy currency of cells. This process is known as oxidative phosphorylation.