What are considered part of the electron transport system?

The electron transport system (ETS) is a series of protein complexes and electron carriers located in the inner mitochondrial membrane in eukaryotes (or the plasma membrane in prokaryotes). It includes four main protein complexes (Complex I, II, III, and IV) and two mobile electron carriers, ubiquinone (Coenzyme Q) and cytochrome c. The ETS facilitates the transfer of electrons from NADH and FADH2 to oxygen, ultimately generating ATP through oxidative phosphorylation. This process also creates a proton gradient across the membrane, which is essential for ATP synthesis.