Mitochondrial ETC — The cytochrome c oxidase complex (Complex IV) performs which set of functions during oxidative phosphorylation?
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AAccepts electrons from cytochrome c (cyt c)
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BTransfers four electrons to O2, reducing it to two molecules of H2O
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CPumps protons from the matrix to the intermembrane space, contributing to the proton gradient
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DAll of these
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EOnly accepts electrons but neither pumps protons nor reduces oxygen
Answer
Correct Answer: All of these
Explanation
Introduction / Context:Complex IV, cytochrome c oxidase, is the terminal enzyme of the mitochondrial electron transport chain. It couples the reduction of oxygen to water with proton translocation, strengthening the proton-motive force used by ATP synthase.
Given Data / Assumptions:
- Electron donor to Complex IV is reduced cytochrome c.
- O2 is the terminal electron acceptor in aerobic respiration.
- Proton pumping by Complex IV is part of chemiosmotic coupling.
Concept / Approach:Evaluate each role: electron acceptance, oxygen reduction, and proton pumping. Complex IV accomplishes all three to complete the chain and maintain the gradient.
Step-by-Step Solution:
cyt c (reduced) → Complex IV → O2 reduction to H2O (four electrons overall).Conformational changes drive proton pumping across the inner membrane.This contributes to membrane potential and pH gradient for ATP synthesis.Verification / Alternative check:Inhibitors like cyanide and carbon monoxide bind Complex IV and block both oxygen consumption and ATP production, demonstrating its roles.
Why Other Options Are Wrong:
e) Contrary to well-established function; Complex IV both reduces O2 and pumps protons.Common Pitfalls:Underestimating Complex IV’s proton pumping; remembering only Complexes I and III pump protons, but IV does as well.
Final Answer:All of these.