The cytochrome complex transfers electrons between which two carrier molecules?
AFrom ferredoxin to plastoquinone
BFrom plastoquinone to plastocyanin
CFrom plastocyanin to plastoquinone
DFrom ubiquinone to cytochrome c
Answer & Solution
Correct answer: B. From plastoquinone to plastocyanin
1. The cytochrome complex is an enzyme composed of two protein complexes.
2. It transfers electrons from the carrier molecule plastoquinone to the protein plastocyanin.
3. Doing so enables both the transfer of protons across the thylakoid membrane and the transfer of electrons from photosystem II to photosystem I.
4. The order matters, since electrons flow from photosystem II onwards rather than backwards.
5. Reversing the two names describes electrons running the wrong way along the chain.
6. Ubiquinone and cytochrome c are the mobile carriers of the mitochondrial chain, not the chloroplast one.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_
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