Q.30 Which one of the following compounds does NOT block electron transport?
(D) Antimycin A
Oligomycin inhibits ATP synthase but allows electron transport to continue, unlike the other ETC blockers. The correct answer is (C) Oligomycin.
Correct Answer
(C) Oligomycin.
Oligomycin blocks F₀ subunit of ATP synthase, preventing proton flow for ATP synthesis (oxidative phosphorylation) but not electron flow through complexes I-IV. ETC continues, building up proton gradient without ATP production.
ETC vs Oxidative Phosphorylation
ETC (Complexes I-IV) transfers electrons from NADH/FADH₂ to O₂, pumping H⁺. ATP synthase uses ΔpH for ATP. True ETC inhibitors halt electron flow; oligomycin uncouples by blocking ATP use of gradient.
Option Breakdown
(A) Cyanide
Incorrect. Binds Complex IV (cytochrome c oxidase), blocking e⁻ transfer to O₂. Stops entire chain, no O₂ consumption.
(B) Rotenone
Incorrect. Inhibits Complex I (NADH-CoQ reductase), preventing e⁻ from NADH to ubiquinone. Blocks NADH oxidation path.
(C) Oligomycin
Correct. Targets ATP synthase F₀, not ETC complexes. Electrons flow, protons accumulate, but no ATP forms.
(D) Antimycin A
Incorrect. Blocks Complex III (cyto b-c1), halting e⁻ from QH₂ to cyt c. Stops mid-chain transfer.
Inhibitor Targets Table
| Compound | Target Complex | Blocks ETC? | Effect |
|---|---|---|---|
| Cyanide (A) | Complex IV | Yes | O₂ binding halted |
| Rotenone (B) | Complex I | Yes | NADH path blocked |
| Oligomycin (C) | ATP Synthase | No | ATP synthesis only |
| Antimycin A (D) | Complex III | Yes | QH₂ to cyt c stop |
