Question:
Which of the following is the "Mobile Electron Carrier" that transfers electrons from Complex III to Complex IV in the Mitochondrial Electron Transport System?
Which of the following is the "Mobile Electron Carrier" that transfers electrons from Complex III to Complex IV in the Mitochondrial Electron Transport System?
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Remember the location differences between the two mobile carriers:
- Ubiquinone (Coenzyme Q) is hydrophobic and resides inside the inner membrane.
- Cytochrome c is hydrophilic and attached to the outer surface of the inner membrane.
- Ubiquinone (Coenzyme Q) is hydrophobic and resides inside the inner membrane.
- Cytochrome c is hydrophilic and attached to the outer surface of the inner membrane.
Updated On: Jun 3, 2026
- Ubiquinone
- Cytochrome c
- NADH dehydrogenase
- ATP synthase
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Question:
The question asks to identify the specific mobile electron transport agent that mediates the transfer of electrons between Complex III and Complex IV within the inner mitochondrial membrane during cellular respiration.
Step 2: Detailed Explanation:
• The Mitochondrial Electron Transport System (ETS) consists of five distinct multi-protein complexes embedded within the inner mitochondrial membrane, along with two specialized mobile electron carriers.
• These complexes transport electrons from metabolic cofactors (NADH and $\text{FADH}_2$) to oxygen, generating a proton gradient that drives ATP synthesis.
• Cytochrome c is a small, soluble, peripheral heme protein loosely attached to the outer surface of the inner mitochondrial membrane (facing the intermembrane space).
• Its primary physiological role is to act as a mobile electron carrier, shuttling electrons from Complex III (Cytochrome $bc_1$ complex) to Complex IV (Cytochrome $c$ oxidase).
• Let us analyze the other options to understand why they are not correct:
- Ubiquinone (A): Also known as Coenzyme Q, this is a lipid-soluble mobile carrier located inside the lipid bilayer. It transfers electrons from Complex I and Complex II to Complex III, not to Complex IV.
- NADH dehydrogenase (C): This is the enzyme that constitutes Complex I, which is fixed in position and initiates electron transport from NADH.
- ATP synthase (D): This is Complex V, which uses the proton-motive force to synthesize ATP and does not act as an electron carrier.
Step 3: Final Answer:
The mobile electron carrier that transfers electrons from Complex III to Complex IV is Cytochrome c.
The question asks to identify the specific mobile electron transport agent that mediates the transfer of electrons between Complex III and Complex IV within the inner mitochondrial membrane during cellular respiration.
Step 2: Detailed Explanation:
• The Mitochondrial Electron Transport System (ETS) consists of five distinct multi-protein complexes embedded within the inner mitochondrial membrane, along with two specialized mobile electron carriers.
• These complexes transport electrons from metabolic cofactors (NADH and $\text{FADH}_2$) to oxygen, generating a proton gradient that drives ATP synthesis.
• Cytochrome c is a small, soluble, peripheral heme protein loosely attached to the outer surface of the inner mitochondrial membrane (facing the intermembrane space).
• Its primary physiological role is to act as a mobile electron carrier, shuttling electrons from Complex III (Cytochrome $bc_1$ complex) to Complex IV (Cytochrome $c$ oxidase).
• Let us analyze the other options to understand why they are not correct:
- Ubiquinone (A): Also known as Coenzyme Q, this is a lipid-soluble mobile carrier located inside the lipid bilayer. It transfers electrons from Complex I and Complex II to Complex III, not to Complex IV.
- NADH dehydrogenase (C): This is the enzyme that constitutes Complex I, which is fixed in position and initiates electron transport from NADH.
- ATP synthase (D): This is Complex V, which uses the proton-motive force to synthesize ATP and does not act as an electron carrier.
Step 3: Final Answer:
The mobile electron carrier that transfers electrons from Complex III to Complex IV is Cytochrome c.
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