Biochemistry 3 Views 1 Answers
Which one of the following statements about the redox reactions of the electron transport chain is correct? 1 NADH gains electrons in the initial reaction of the electron transport chain. 2 The electron transport chain takes electrons from water and gives them to oxygen. 3 The oxidation of NADH is directly coupled to the reduction of oxygen to water. 4 The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane. 5 The redox reactions of the electron transport chain are directly coupled with the synthesis of ATP.
Which one of the following statements about the redox reactions of the electron transport chain is correct? 1 NADH gains electrons in the initial reaction of the electron transport chain. 2 The electron transport chain takes electrons from water and gives them to oxygen. 3 The oxidation of NADH is directly coupled to the reduction of oxygen to water. 4 The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane. 5 The redox reactions of the electron transport chain are directly coupled with the synthesis of ATP.
Answered
The correct statement is:
4. The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.
Explanation:
- Statement 1 (Incorrect): NADH loses electrons (is oxidized) in the initial reaction of the electron transport chain, not gains them. NADH donates electrons to Complex I of the ETC.
- Statement 2 (Incorrect): The electron transport chain takes electrons from NADH and FADH2_2 (not water) and transfers them through various complexes, eventually passing them to oxygen, which is reduced to water.
- Statement 3 (Incorrect): The oxidation of NADH (which donates electrons to Complex I) is not directly coupled to the reduction of oxygen. Oxygen is the final electron acceptor in the chain, but NADH’s oxidation occurs earlier in the process, and its electrons travel through several complexes before reducing oxygen.
- Statement 4 (Correct): The redox reactions in the electron transport chain result in the transfer of electrons through the complexes, which releases energy. This energy is used to pump protons (H+^+) across the inner mitochondrial membrane, creating a proton gradient, which is essential for ATP synthesis.
- Statement 5 (Incorrect): While the movement of protons across the membrane (and the resulting proton gradient) drives ATP synthesis, the redox reactions themselves are not directly coupled with ATP synthesis. ATP is synthesized by ATP synthase, which is powered by the proton gradient created by the electron transport chain.
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