 Electron carrier

An electron carrier cycles between oxidation and reduction. Ubiquinone carries two Electrons, while cytochrome c carries one at a time.^[ref]

For example, transferring the two Electrons supplied by one NADH requires two one-Electron deliveries by cytochrome c. It does not require two permanently consumed cytochrome c molecules: an available electron carrier can unload, return and reload. Electron carriers recycle material while the net redox conversion supplies free energy.