1.  Give and accept. Distinguish between an oxidizing agent and a reducing agent. ✓ 1

2.  Like mac and cheese. Match each term with its description. ✓ 1

3.  Reference states. The standard oxidation–reduction potential for the reduction of O₂ to H₂O is given as 0.82 V in Table 20.1. However, the value given in textbooks of chemistry is 1.23 V. Account for this difference. ✓ 1

4.  Thermodynamic constraint. Compare the ΔG°′ values for the oxidation of succinate by NAD⁺ and by FAD. Use the data given in Table 20.1, and assume that E′₀ for the FAD–FADH₂ redox couple is nearly 0 V. Why is FAD rather than NAD⁺ the electron acceptor in the reaction catalyzed by succinate dehydrogenase? ✓ 1

5.  Hitchin’ a ride. What is the evidence that modern mitochondria arose from a single endosymbiotic event?

6.  Benefactor and beneficiary. Identify the oxidant and the reductant in the following reaction:

7.  Location, location, location. Iron is a component of many of the electron carriers of the electron-transport chain. How can it participate in a series of coupled redox reactions if the Δ E′₀ value is +0.77 V as seen in Table 20.1? ✓ 1 ✓ 2

8.  Six of one, half dozen of the other. How is the redox potential (ΔE′0) related to the free-energy change of a reaction (ΔG°′)? ✓ 1

9.  Structural considerations. Explain why coenzyme Q is an effective mobile electron carrier in the electron-transport chain. ✓ 1

10.  Line up. Place the following components of the electron-transport chain in their proper order: (a) cytochrome c; (b) Q-cytochrome c oxidoreductase; (c) NADH-Q oxidoreductase; (d) cytochrome c oxidase; (e) ubiquinone. ✓ 2

11.  Like Dolce and Gabbana. Match the terms on the left with those on the right.

12.  ROS, not ROUS. What are the reactive oxygen species, and why are they especially dangerous to cells?

13.  Inhibitors. Rotenone inhibits electron flow through NADH-Q oxidoreductase. Antimycin A blocks electron flow between cytochromes b and c₁. Cyanide blocks electron flow through cytochrome oxidase to O₂. Predict the relative oxidation–reduction state of each of the following respiratory-chain components in mitochondria that are treated with each of the inhibitors: NAD⁺; NADH-Q oxidoreductase; coenzyme Q; cytochrome c₁; cytochrome c; cytochrome a. ✓ 1

14.  Efficiency. What is the advantage of having Complexes I, III, and IV associated with one another in the form of a respirasome? ✓ 2

15.  Recycling device. The cytochrome b component of Q-cytochrome c oxidoreductase enables both electrons of QH₂ to be effectively utilized in generating a proton-motive force. Cite another recycling device in metabolism that brings a potentially dead-end reaction product back into the mainstream.

16.  Maybe you shouldn’t take your vitamins. Exercise is known to increase insulin sensitivity and to ameliorate type 2 diabetes. Recent research suggests that taking antioxidant vitamins might mitigate the beneficial effects of exercise with respect to ROS protection.

(a) What are antioxidant vitamins?

(b) How does exercise protect against ROS?

(c) Explain why vitamins might counteract the effects of exercise.

17.  Linked In. What citric acid cycle enzyme is also a component of the electron-transport chain?

18.  Breathe or ferment? Compare fermentation and respiration with respect to electron donors and electron acceptors.

19.  Weaker electrons. Electrons from NADH pump more protons as a consequence of reaction with oxygen than do the electrons from FADH₂. Calculate the energy released by the reduction of O₂ with FADH₂. ✓ 2

20.  Crossover point. The precise site of action of a respiratory-chain inhibitor can be revealed by the crossover technique. Britton Chance devised elegant spectroscopic methods for determining the proportions of the oxidized and reduced forms of each carrier. This determination is feasible because the forms have distinctive absorption spectra, as illustrated in the adjoining graph for cytochrome c. You are given a new inhibitor and find that its addition to respiring mitochondria causes the carriers between NADH and QH₂ to become more reduced and those between cytochrome c and O₂ to become more oxidized. Where does your inhibitor act? ✓ 2