Unit 5: Metabolism II - Practice Quiz

1 In which cellular location does the citric acid cycle occur in eukaryotes?

2 Which molecule combines with oxaloacetate to form citrate in the first step of the citric acid cycle?

3 How many molecules of are produced in one complete turn of the citric acid cycle?

4 Which of the following is the only step in the citric acid cycle that directly produces a high-energy phosphate bond via substrate-level phosphorylation?

5 The glyoxylate cycle allows organisms to synthesize carbohydrates from which type of molecule?

6 Which two enzymes are unique to the glyoxylate cycle and not present in the citric acid cycle?

7 In plants, the glyoxylate cycle takes place primarily in which organelle?

8 The glyoxylate cycle bypasses which two steps of the citric acid cycle?

9 Where is the electron transport chain located in eukaryotic cells?

10 What is the final electron acceptor of the mitochondrial electron transport chain?

11 Which mobile electron carrier transfers electrons from Complex III to Complex IV?

12 Which complex of the electron transport chain accepts electrons directly from ?

13 Which enzyme uses the proton gradient to synthesize ATP during oxidative phosphorylation?

14 The theory explaining how the proton gradient drives ATP synthesis is called the:

15 Approximately how many ATP molecules are generated per oxidized through the electron transport chain?

16 Which molecule acts as an uncoupler, allowing electron transport to continue while stopping ATP synthesis by dissipating the proton gradient across the inner mitochondrial membrane?

17 The process by which fatty acids are broken down two carbons at a time is called:

18 Which molecule shuttles long-chain fatty acids across the inner mitochondrial membrane for oxidation?

19 Fatty acid biosynthesis occurs mainly in which part of the cell?

20 Which of the following is a ketone body?

21 During one complete turn of the citric acid cycle, how many molecules of , , and are produced per acetyl-CoA?

22 Which enzyme of the citric acid cycle is the only one embedded in the inner mitochondrial membrane and also participates directly in the electron transport chain?

23 A cell is treated with fluoroacetate, which is converted to fluorocitrate and inhibits aconitase. Which metabolite would you expect to accumulate?

24 The conversion of -ketoglutarate to succinyl-CoA is analogous in mechanism to which other reaction?

25 The glyoxylate cycle allows plants and microorganisms to synthesize carbohydrates from fatty acids by bypassing which two -releasing steps of the TCA cycle?

26 Which two enzymes are unique to the glyoxylate cycle and not found in the standard citric acid cycle?

27 In plant seeds, the glyoxylate cycle takes place primarily in which organelle?

28 Which of the following correctly orders the mobile electron carriers and complexes in the sequence of electron flow?

29 Rotenone blocks electron transfer at Complex I. Electrons from which substrate can still be oxidized to sustain some ATP production?

30 Which complex does NOT pump protons across the inner mitochondrial membrane?

31 The standard reduction potential () values increase along the chain. What does this trend indicate about electron flow?

32 According to the chemiosmotic theory, ATP synthase is driven directly by which of the following?

33 2,4-Dinitrophenol (DNP) acts as an uncoupler. What is its effect on mitochondrial function?

34 Complete oxidation of one molecule of via the ETC yields approximately how many ATP under the currently accepted (P/O) ratio?

35 How many rounds of -oxidation and how many acetyl-CoA molecules are produced from the complete oxidation of palmitic acid (C16)?

36 The transport of long-chain fatty acyl groups into the mitochondrial matrix depends on which carrier molecule?

37 Which statement correctly distinguishes fatty acid biosynthesis from -oxidation?

38 The committed and rate-limiting step of fatty acid synthesis is the carboxylation of acetyl-CoA to malonyl-CoA. Which cofactor does this enzyme require?

39 Which of the following is NOT considered a ketone body?

40 During prolonged starvation, ketone bodies become a major fuel for the brain. Why can the liver produce but not utilize ketone bodies?

41 During one turn of the citric acid cycle, the carbon atoms released as are derived from oxaloacetate rather than the acetyl group that entered. Which enzymatic steps release these two molecules?

42 The citric acid cycle is not strictly a catabolic pathway because several intermediates are withdrawn for biosynthesis (cataplerosis). If -ketoglutarate is continuously removed for amino acid synthesis, which anaplerotic reaction most directly replenishes the cycle?

43 Fluoroacetate is toxic because it is converted to fluorocitrate, which inhibits aconitase. What is the immediate metabolic consequence of this inhibition?

44 The only step of the citric acid cycle occurring within the inner mitochondrial membrane, directly feeding electrons into the respiratory chain via , is catalyzed by:

45 The glyoxylate cycle allows plants and some microbes to achieve net synthesis of carbohydrate from acetyl-CoA, something animals cannot do. This is possible because the glyoxylate cycle bypasses the two decarboxylation steps of the citric acid cycle using which pair of enzymes?

46 For each turn of the glyoxylate cycle, how many acetyl-CoA molecules are consumed, and what is the net four-carbon product available for gluconeogenesis?

47 In germinating oilseeds, the glyoxylate cycle is compartmentalized. Which statement about its subcellular organization is correct?

48 Antimycin A blocks electron flow at Complex III (between cytochrome and cytochrome ). In an isolated mitochondrial preparation given antimycin A, adding which substrate/electron acceptor pair could still support some electron transport?

49 The Q cycle at Complex III explains an apparently inefficient bifurcated electron path. What is the net proton translocation across the inner membrane per two electrons passing through Complex III via the Q cycle?

50 Rotenone inhibits Complex I. If mitochondria are supplied with succinate (not NADH-linked substrate) in the presence of rotenone, what is the expected outcome?

51 Uncouplers such as 2,4-dinitrophenol (DNP) dissipate the proton gradient. Which combination of effects best describes DNP action on actively respiring mitochondria?

52 Given the chemiosmotic model, oligomycin binds the subunit of ATP synthase. In tightly coupled mitochondria, what happens to electron transport shortly after oligomycin addition, and why?

53 The P/O ratio for NADH oxidation is approximately 2.5 rather than the older integer value of 3. This non-integer value arises because:

54 Complete -oxidation of palmitate (C16) yields how many acetyl-CoA, and requires how many rounds of the -oxidation spiral?

55 Oxidation of odd-chain and unsaturated fatty acids requires additional enzymes. Which extra reactions/cofactors are needed to fully oxidize an odd-chain fatty acid?

56 Fatty acid synthesis and -oxidation are reciprocally regulated. Malonyl-CoA, the committed intermediate of synthesis, also inhibits which enzyme to prevent simultaneous oxidation?

57 Fatty acid biosynthesis in the cytosol requires acetyl-CoA, which is generated in mitochondria. The citrate-malate shuttle transfers acetyl units to the cytosol and also provides part of the reducing power. Which by-product of this shuttle supplies cytosolic NADPH?

58 During prolonged starvation, the liver exports ketone bodies but cannot use them itself. Which enzyme, absent in liver, is required by peripheral tissues to activate acetoacetate for oxidation?

59 Excessive ketone body production in uncontrolled diabetes leads to ketoacidosis. Which underlying metabolic imbalance most directly drives the overproduction of acetyl-CoA channeled into ketogenesis?

60 The three physiologically relevant ketone bodies are acetoacetate, -hydroxybutyrate, and acetone. Which statement about them is correct?