Most of the activity of the electron transport chain occurs in a cell's mitochondrial inner membrane. This is where the electron transport chain gets the proteins it needs to function properly.
The electron transport chain is the final step of cellular respiration. During this step, electrons are stripped from FADH2 and NADH. They are then transferred to oxygen molecules to produce water. The electron transport chain relies on three integral membrane protein complexes to function properly: NADH dehydrogenase complex, cytochrome c reductase complex and cytochrome c oxidase complex. Most of the ATP produced during cellular respiration is generated by the electron transport chain.