As high-energy electrons flow down the electron transport chain, energy is released. What is this energy used to do?
The correct answer and explanation is :
As high-energy electrons flow down the electron transport chain (ETC) in cellular respiration, the energy released is used to pump protons (H⁺ ions) across the inner mitochondrial membrane, creating a proton gradient (proton motive force).
Explanation:
The electron transport chain (ETC) is the final stage of aerobic respiration, occurring in the inner mitochondrial membrane. It consists of a series of protein complexes (Complexes I–IV) and mobile electron carriers (ubiquinone and cytochrome c). The electrons come from NADH and FADH₂, which were produced in earlier stages of respiration (glycolysis, the Krebs cycle).
- Electron Flow and Energy Release:
- Electrons from NADH enter Complex I, while those from FADH₂ enter Complex II.
- These electrons are passed down the chain through redox reactions.
- As electrons move, they lose energy at each step.
- Proton Pumping:
- The released energy is used by Complexes I, III, and IV to actively transport H⁺ ions from the mitochondrial matrix into the intermembrane space.
- This creates an electrochemical gradient (proton motive force), with a high concentration of H⁺ ions outside the inner membrane and a low concentration inside.
- ATP Synthesis:
- The stored energy in the proton gradient is harnessed by ATP synthase, an enzyme embedded in the inner membrane.
- As H⁺ ions flow back into the matrix through ATP synthase (down their gradient), the enzyme catalyzes the formation of ATP from ADP and Pi.
This entire process, known as oxidative phosphorylation, is how most ATP is generated in aerobic respiration, making it essential for cellular energy production.