How does the electron-carrying capacity of cytochrome c differ from that of ubiquinone?
ACytochrome c accepts only one electron at a time
BCytochrome c accepts four electrons at a time
CCytochrome c accepts no electrons, only protons
DCytochrome c accepts electrons and oxygen jointly
Answer & Solution
Correct answer: A. Cytochrome c accepts only one electron at a time
1. Complex III passes its electrons to cytochrome c for transport to the fourth complex.
2. Cytochrome c is the acceptor of electrons from ubiquinone.
3. Ubiquinone carries pairs of electrons, but cytochrome c can accept only one at a time.
4. So a pair delivered by ubiquinone has to be split across two separate handovers.
5. Saying it carries protons rather than electrons confuses the carrier with the pumps that move hydrogen ions.
6. Oxygen is bound only at the fourth complex, held between iron and copper ions, and never by cytochrome c in transit.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.4 Oxidative Phosphorylation_
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