The electron transport chain is found in the inner mitochondrial membrane of eukaryotic cells and in the plasma membrane of prokaryotic cells. Here’s a simplified overview of its function:

1. Electron Donors and Acceptors: The chain consists of a series of electron donors and acceptors. In mitochondria, these include complexes I, II, III, and IV, as well as other molecules like ubiquinone and cytochrome c.

2. Redox Reactions: Electrons are passed along the chain from one carrier molecule to another in a series of redox reactions. These electrons are originally provided by NADH and FADH2, which are generated during other stages of cellular respiration.

3. Proton Gradient: As electrons move through the chain, protons are pumped from the mitochondrial matrix into the intermembrane space. This creates a concentration gradient and an electrochemical gradient (often referred to as the proton motive force).

4. ATP Synthesis: The electrochemical gradient drives protons back across the membrane through the enzyme ATP synthase. This enzyme uses the flow of protons to generate ATP from ADP and inorganic phosphate. This process is known as oxidative phosphorylation.

5. Oxygen’s Role: In aerobic organisms, the final electron acceptor at the end of the electron transport chain is molecular oxygen (O2). Oxygen accepts electrons and takes up protons to form water.