Final answer:
The electron transport chain includes four protein complexes labeled I through IV and two mobile electron carriers that facilitate the transfer of electrons from substrates like NADH and FADH2 to oxygen. Complex I and II receive electrons from NADH and FADH2, respectively, while Complex III and IV continue the electron transport and contribute to ATP synthesis through a proton gradient.
Step-by-step explanation:
The electron transport chain (ETC) or respiratory chain is a crucial part of aerobic respiration and is located in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. This chain consists of four main protein complexes (I-IV) which work together to transfer electrons from donors like NADH and FADH2 to the final electron acceptor, which is oxygen, resulting in the production of water.
Complex I, also known as NADH-coenzyme Q oxidoreductase, is the first complex in the ETC. It accepts electrons from NADH, transferring them to Coenzyme Q (CoQ), while pumping protons across the membrane to generate a proton gradient used for ATP synthesis. Complex II, succinate-coenzyme Q oxidoreductase, obtains electrons from FADH2 resulting from the citric acid cycle but unlike Complex I, it does not pump protons.
Complex III, cytochrome b-c1 complex, transfers electrons from CoQ to cytochrome c, while continuing to pump protons. Finally, Complex IV or cytochrome c oxidase receives electrons from cytochrome c and transfers them to oxygen, the final electron acceptor, to form water, and this complex also pumps protons to aid in the production of ATP.
The released energy at three points in the ETC is used to pump protons across a membrane, contributing to the chemiosmotic gradient essential for ATP synthesis in a process known as oxidative phosphorylation.