18-21

16. Which of the following answers completes the sentence more correctly? The rate of flow of electrons through the electron transport chain is most directly regulated by (a) the ATP:ADP ratio. (b) the concentration of acetyl CoA. (c) the rate of oxidative phosphorylation. (d) feedback inhibition by H2O. (e) the catalytic rate of cytochrome oxidase.

(a) the ATP:ADP ratio.

11. Considering the citric acid cycle steps between α-ketoglutarate and malate, how many high-energy phosphate bonds, or net ATP molecules, can be generated? (a) 4 (d) 10 (b) 5 (e) 12 (c) 7

(b) 5

6. Which of the following answers complete the sentence correctly? The pyruvate dehydrogenase complex is activated by: (a) phosphorylation of the pyruvate dehydrogenase component (E1). (b) stimulation of a specific phosphatase by Ca2+. (c) inhibition of a specific kinase by pyruvate. (d) decrease of the NADH/NAD+ ratio. (e) decreased levels of insulin.

(b) stimulation of a specific phosphatase by Ca2+. (c) inhibition of a specific kinase by pyruvate. (d) decrease of the NADH/NAD+ ratio

12. The standard free-energy change (in terms of net ATP production) when glucose is converted to 6 CO2 and 6 H2O is about how many times as great as the free-energy change when glucose is converted to two lactate molecules? (a) 2 (c) 15 (b) 7 (d) 28

(c) 15 Ans: c. From glucose to lactate, two ATP are formed; from glucose to CO2 and H2O, about 30 ATP are formed

27. How many ATP molecules are generated during the complete oxidative degradation of each of the following to CO2 and H2O? Assume that the glycerol phosphate shuttle is operating. (a) acetyl CoA (b) phosphoenolpyruvate (c) glyceraldehyde 3-phosphate

Ans: (a) About 10 ATP: citric acid cycle (3 NADH → 2.5, 1 FADH2 → 1.5, and 1 GTP) (b) About 13.5 ATP: citric acid cycle (10 ATP), pyruvate dehydrogenase reaction (1 NADH, intramitochondrial → 2.5), pyruvate kinase reaction (1 ATP) (c) About 16 ATP: citric acid cycle (10 ATP), pyruvate dehydrogenase reaction (1 NADH → 2.5), pyruvate kinase reaction (1 ATP), phosphoglycerate kinase reaction (1 ATP), glyceraldehyde 3-phosphate dehydrogenase reaction (1 NADH, extramitochondrial, which yields 1.5 ATP by the glycerol phosphate shuttle)

13. Although the ATP/ADP ratio and the availability of substrates and cycle intermediates are very important factors affecting the rate of the citric acid cycle, the NADH/NAD ratio is of paramount importance. Explain why

Ans: The oxidized cofactors NAD and FAD are absolutely required as electron acceptors in the various dehydrogenation reactions of the citric acid cycle. When these oxidized cofactors are not available, as when their reoxidation is inhibited in the absence of O2 or respiration, the citric acid cycle is also inhibited.

29. Proton gradients are used for which of the following? (a) generating heat (b) free-energy storage (c) ATP generation (d) active transport (e) mechanical movement

Ans: a, b, c, d, e. Answer (b) is correct, but you should realize that free-energy storage by a proton gradient across a membrane is more transient than storage in a molecule such as glucose or NADH.

22. Which of the following experimental observations provide evidence that supports the chemiosmotic model of oxidative phosphorylation? (a) A closed membrane or vesicle compartment is required for oxidative phosphorylation. (b) A system of bacteriorhodopsin and ATPase can produce ATP in synthetic vesicles when light causes proton pumping. (c) A proton gradient is generated across the inner membrane of mitochondria during electron-transport. (d) ATP is synthesized when a proton gradient is imposed on mitochondria.

Ans: a, b, c, d. Answer (d) is true, although not mentioned in the text all of the above

21. Which of the following constitute cellular respiration? (a) biosynthesis of glycogen in the liver and muscles (b) conversion of an electron-motive force into a proton-motive force (c) formation of compounds with high electron transfer potential (d) conversion of a proton-motive force into a phosphoryl-transfer force

Ans: b, c, d. Although glycogen is a molecule that stores energy, answer (a) is incorrect because respiration is defined as the collection of reactions that use the reductive power of NADH and FADH2 to form ultimately ATP

26. Approximately how many ATP are formed for each extramitochondrial NADH that is oxidized to NAD by O2 via the electron transport chain. Assume that the glycerol phosphate shuttle is operating. (a) 1.0 (c) 2.5 (b) 1.5 (d) 3.0

B) The oxidation of NADH by the electron transport chain leads to the synthesis of approximately 2.5 ATP. However, when the reducing equivalents of an extramitochondrial NADH enter the mitochondrial matrix via the glycerol phosphate shuttle, they give rise to FADH2, which yields 1.5 ATP

5. What are the allosteric inhibitors of the pyruvate dehydrogenase complex?

It makes it easy to remember the inhibitors if you notice that they are the products of the reaction. Acetyl CoA and NADH are the immediate products, and high ATP is an eventual product. Normally "feedback inhibition" involves a product from several steps farther down a pathway, but this is a true allosteric inhibition and not a simple "product inhibition" based on the principle of mass action.

28. What is meant by the term respiratory control?

The regulation of the rate of oxidative phosphorylation by the availability of ADP is referred to as respiratory control.

15. Which of the following describes the direction of proton movement relative to electron transfer and phosphorylation? a) Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the matrix. b) Electron transfer pumps protons into the matrix. As the protons leave the matrix through the ATP synthase, ATP is produced on the opposite side of the membrane. c) Electron transfer pumps protons into the matrix. As the protons leave the matrix through the ATP synthase, ATP is produced in the matrix. d) Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the intermembrane space.

a) Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the matrix.

14. In order for an electron transfer reaction to be energetically spontaneous, which of the following must be TRUE? a) The change in reduction potential, ΔEo, must be positive. b) The change in reduction potential, ΔEo, must be negative. c) The two groups involved in the electron transfer must be in direct contact. d) There must be a concurrent increase in entropy.

a) The change in reduction potential, ΔEo, must be positive.

7. Although the pyruvate dehydrogenase complex is subject to allosteric control, especially inhibition by reaction products, the main regulatory process controlling the enzyme's activity in eukaryotes is a) phosphorylation by ATP that turns off the complex and dephosphorylation that turns it on. b) phosphorylation by ATP that turns on the complex and dephosphorylation that turns it off. c) exchange of ADP and ATP on the pyruvate dehydrogenase complex. d) AMP binding to the enzyme and activating it.

a) phosphorylation by ATP that turns off the complex and dephosphorylation that turns it on.

17. Consider a substance that can exist in an oxidized form X and a reduced form X-. Such a pair is called a(n): a) redox couple b) reduction couple c) electron-transfer potential d) half-cell

a) redox couple

10. Which of the following answers complete the sentence correctly? Succinate dehydrogenase (a) transfers electrons directly to coenzyme Q. (b) contains FAD and NAD cofactors like pyruvate dehydrogenase. (c) is an integral membrane protein unlike the other enzymes of the citric acid cycle. (d) carries out an oxidative decarboxylation like isocitrate dehydrogenase.

a) transfers electrons directly to coenzyme Q. c) is an integral membrane protein unlike the other enzymes of the citric acid cycle.

23. Which of the following statements about the mitochondrial ATP-synthesizing complex are correct? (a) It contains more than 10 subunits. (b) It is located in the intermembrane space of mitochondria. (c) It contains a subassembly that constitutes the proton channel. (d) It is sensitive to oligomycin inhibition. (e) It translocates ATP through the mitochondrial membranes.

a,c,d

1. Which of the following is NOT a product of the reaction catalyzed by pyruvate dehydrogenase complex? a) NADH b) pyruvate c) CO2 d) acetyl CoA

b) pyruvate

3. Entry to the citric acid cycle involves the generation of acetyl CoA. The enzyme that catalyzes the production of acetyl CoA is _____. This enzyme is negatively regulated by _____ in a high-energy charge situation. a) citrate synthase; ATP b) pyruvate dehydrogenase; NADH c) α-ketoglutarate dehydrogenase complex; ATP d) α-ketoglutarate dehydrogenase complex; NADH

b) pyruvate dehydrogenase; NADH

25. Which of the following pairs of molecules are transported in opposition to each other across the mitochondrial membrane in the malate-aspartate shuttle? (a) Malate and aspartate (b) Aspartate and glutamate (c) Malate and α-ketoglutarate (d) Malate and glutamate (e) Oxaloacetate and glutamate

b,c While all of the molecules listed except oxaloacetate are transported in the shuttle, only certain pairs are transported through the same protein in opposition to each other.

19. Which of the following is NOT a part of the Mitchell chemiosmotic hypothesis? a) A portion of the energy from electron transport is used in generation of a proton-motive force that in turn provides the energy for ATP synthesis. b) The use of electron transfer to provide the energy for ATP synthesis requires an intact membrane. c) High-energy phosphorylated intermediates that serve as phosphate donors to ADP are generated as a result of electron-transfer reactions. d) ATP production is driven by the formation of a gradient of protons between the matrix (low proton concentration) and the intermembrane space (high proton concentration).

c) High-energy phosphorylated intermediates that serve as phosphate donors to ADP are generated as a result of electron-transfer reactions.

8. Assuming that pyruvate was labeled with radioactive 14C in its middle (keto) carbon, where would the radiolabel appear after one turn of the citric acid cycle? a) as CO2 b) in one carboxyl group of oxaloacetate c) equally divided between the two carboxyl groups of oxaloacetate d) on the methylene carbon (-CH2-) of oxaloacetate

c) equally divided between the two carboxyl groups of oxaloacetate

20. The process of glycolysis occurs in the cytoplasm. The electrons from the NADH generated during glycolysis a) enter the mitochondrial electron chain directly as NADH freely enters the mitochondria. b) cannot be used by the mitochondrial electron transport chain as NADH cannot enter the mitochondria. c) may enter the electron transport chain either at the level of NADH or FADH2, depending on the shuttle system used to transport them into the mitochondria. d) will always be able to produce the same number of ATP via oxidative phosphorylation as mitochondrial NADH electrons.

c) may enter the electron transport chain either at the level of NADH or FADH2, depending on the shuttle system used to transport them into the mitochondria.

9. Oxygen is not used at any point in the citric acid cycle. However, the cycle will not work without oxygen because a) molecular O2 will regulate many of the enzyme steps. b) oxygen is necessary to transcribe and translate enzymes for the reactions. c) oxygen is needed to regenerate electron carriers. d) not enough energy is generated without O2 to run the cycle.

c) oxygen is needed to regenerate electron carriers.

18. Which of the following statements points to the endosymbiotic event yielding intercellular mitochondria? a) Mitochondria contain their circular DNA. b) Mitochondria have a double membrane. c) Mitochondria contain specific transcription and translation machinery. d) All of the above

d) All of the above

4. The pyruvate dehydrogenase complex is regulated by: a) phosphorylation. b) allosteric interactions. c) covalent modifications. d) All of the above

d) All of the above

16. For a given reduced/oxidized molecular pair (X-/X), a negative reducing potential suggests that the a) X- has a higher affinity for the electrons than X does. b) X has a higher affinity for electrons than H2 does. c) X- has a lower affinity for the electrons than X does. d) X has a lower affinity for electrons than H2 does.

d) X has a lower affinity for electrons than H2 does.

2. Which of the following is NOT a coenzyme necessary in the function of pyruvate dehydrogenase complex? a) lipoic acid b) FAD c) NAD+ d) ubiquinone

d) ubiquinone

24. ATP synthase can form ATP in the absence of a proton gradient when it is mixed with ADP and Pi. Explain what is the energy of the proton gradient used for.

the energy of the proton gradient is used for release of ATP, and not for the ATP synthesis.