A patient with a mitochondrial disorder has a mutation affecting cytochrome c. Which process is most directly impaired?

• A Transfer of electrons from NADH to Complex I
• B Transfer of electrons from Complex II to ubiquinone
• C Transfer of electrons from Complex III to Complex IV ✓
• D Synthesis of ATP by the F1 subunit of ATP synthase

Explanation

Cytochrome c is a soluble peripheral membrane protein that shuttles electrons from Complex III (cytochrome bc1) to Complex IV (cytochrome c oxidase). A cytochrome c defect would impair this inter-complex transfer. Distractor A is wrong because NADH transfers electrons directly to Complex I. Distractor B is wrong because Complex II transfers electrons to ubiquinone, not cytochrome c. Distractor D is wrong because ATP synthesis requires proton flow, not cytochrome c directly.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.