Electrons cannot be passed through unless the protons are translocated at the same time. The energy used to force the protons across the inner membrane is released by the passage of the electron pair from NADH to coenzyme Q. The electrons are then passed through complex III, where more protons are forced across, and complex IV, where still more protons are forced across. Complex IV, called cytochrome oxidase, uses the energy it receives along with an electron pair to reduce oxyen to water. Note that since molecular oxygen is diatomic it takes two cytochrome oxidase complexes, two electron pairs, and four hydrogen ions to complete the reaction.