Question

Components of the mitochondrial Electron Transport Chain (ETC):
A. NADH-Coenzyme Q oxidoreductase
B. Cytochrome \(bc_1\) complex
C. Ubiquinone
D. Cytochrome C
E. Cytochrome C Oxidase
Choose the correct sequence of electron transfer through the aforementioned components of the mitochondrial ETC

• A. A, B, C, D, E
• B. A, C, B, D, E
• C. A, D, B, C, E
• D. A, B, D, C, E

Hint:

To remember the sequence, focus on the mobile carriers that link the large complexes: Complex I (A) passes electrons to the lipid carrier Ubiquinone (C), which links to Complex III (B), which passes electrons to the soluble carrier Cytochrome C (D), which links to Complex IV (E).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The mitochondrial electron transport chain (ETC) consists of four membrane-bound multi-protein complexes (Complexes I to IV) and two mobile electron carriers (ubiquinone and cytochrome c).
Electrons flow spontaneously through these components in order of increasing redox potential, releasing energy used to pump protons across the inner membrane.

Step 2: Detailed Explanation:
Let us trace the path of electron transfer starting from NADH:
1. NADH-Coenzyme Q oxidoreductase (Complex I - A): This complex accepts two electrons from NADH and transfers them to the mobile lipid-soluble carrier, ubiquinone.
2. Ubiquinone (Coenzyme Q - C): This hydrophobic mobile carrier in the lipid bilayer accepts electrons from Complex I (and Complex II) and diffuses through the membrane to deliver them to Complex III.
3. Cytochrome \(bc_1\) complex (Complex III - B): This complex accepts electrons from reduced ubiquinone (\(\text{QH}_2\)) and transfers them via the Q-cycle to the mobile hydrophilic carrier, cytochrome c.
4. Cytochrome C (D): This water-soluble mobile peripheral protein carries one electron at a time from Complex III to Complex IV along the intermembrane space.
5. Cytochrome C Oxidase (Complex IV - E): This final complex accepts electrons from cytochrome c and transfers them to the terminal electron acceptor, molecular oxygen (\(\text{O}_2\)), reducing it to water (\(\text{H}_2\text{O}\)).
Therefore, the correct sequential flow of electrons is: A \(\to\) C \(\to\) B \(\to\) D \(\to\) E.

Step 3: Final Answer:
The correct sequence of electron transfer is A, C, B, D, E, which corresponds to option (B).