Questions:

1. Concerning the TCA cycle, all of the following are true EXCEPT
  1. The TCA cycle is also called the citric acid cycle and the Krebs cycle
  2. Acetyl CoA and NAD+ are substrates
  3. Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase are control enzymes
  4. NADH, ATP, and Ca++ are all allosteric effectors of the control enzymes
  5. The cycle is in the cytosol of most tissues in your body
2. Which of the following is NOT a dehydrogenase (oxidoreductase) in the TCA cycle?
  1. Isocitrate dehydrogenase
  2. Alpha-ketoglutarate dehydrogenase
  3. Pyruvate dehydrogenase
  4. Succinate dehydrogenase
  5. Malate dehydrogenase
3. When one molecule of acetyl CoA is oxidized by the TCA cycle and oxidative phosphorylation, the approximate energy yield is the equivalent of
  1. 6 ATP
  2. 8 ATP
  3. 10 ATP
  4. 20 ATP
  5. 24 ATP
4. The enzyme in the TCA cycle that catalyzes a substrate level phosphorylation is
  1. Citrate synthase
  2. Isocitrate dehydrogenase
  3. Succinate thiokinase
  4. Succinate dehydrogenase
  5. 3-Phosphoglycerate kinase
5. A difference between substrate level phosphorylation and oxidative phosphorylation is that substrate level phosphorylation
  1. Does not take place in the mitochondria
  2. Produces ATP as a product
  3. Only happens when oxygen is absent
  4. Does not need inorganic phosphate as a substrate
  5. Occurs in the absence of molecular oxygen
6. All of the following statements are true EXCEPT
  1. FADH2 binds tightly to its apoenzyme to form the holoenzyme
  2. FADH2 does not dissociate and travel free in solution
  3. FADH2 is a good feed back inhibitor
  4. NADH is stable in solution and only reacts with enzymes
  5. NADH is a good feed back inhibitor
7. All of the following are true EXCEPT
  1. Acetyl CoA and Succinyl CoA contain thioester bonds
  2. Thioester bonds are high energy bonds
  3. Thioester bonds have a large negative ΔG0' of hydrolysis
  4. When the thioester bond of acetyl CoA is cleaved in the citrate synthase reaction, the energy is released, giving the reaction a large negative ΔG0' of –8 kcal/mole
  5. Reactions with large negative ΔG0' tend to be reversible
8. All of the following are correct EXCEPT.  The α-ketoglutarate complex contains the cofactor
  1. Thiamin pyrophosphate derived from the vitamin thiamine
  2. Lipoate derived from the vitamin lipoid
  3. CoA derived from the vitamin pantothenate
  4. NADH derived from the vitamin niacin
  5. FAD derived from the vitamin riboflavin
9. Chose the best answer.  Several enzyme reactions in the TCA cycle are considered irreversible because
  1. The products do not rise to high enough concentrations to overcome the large negative ΔG0' values for the reactions
  2. The substrates of the enzymes never reach concentrations low enough to overcome the large negative ΔG0' values for the reactions
  3. Because the reactions have a large negative ΔG
  4. Both A and B are correct
  5. A, B, and C could all be correct
10. Given the following enzyme pathway, A→B→C→D

And given that the ΔG0‘ for A→B is –7; for B→C is +4; for C→D is +1

Then the ΔG0‘ for A→D is

  1. +5
  2. +2
  3. 0
  4. -1
  5. -2
11. When Ca++ increases in muscle cells, muscle contracts and all of the following happen EXCEPT

  1. The concentration of AMP and ADP increase and the concentration of ATP decreases
  2. The oxidation of NADH and FADH2 by the electron transport chain increases
  3. Isocitrate dehydrogenase and α-keto glutarate dehydrogenase are allosterically activated by increases in Ca++
  4. Isocitrate dehydrogenase and alpha-keto glutarate dehydrogenase are allosterically activated by increases in NADH
  5. Isocitrate dehydrogenase is allosterically activated by increases in ADP
12. The two most important control enzymes of the TCA cycle are
  1. Isocitrate dehydrogenase and fumarase
  2. Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase
  3. α-ketoglutarate dehydrogenase and fumarase
  4. Fumarase and succinate thiokinase
  5. Fumarase and citrate synthase
13. All of the following are major dietary sources of Acetyl CoA EXCEPT
  1. Carbohydrates
  2. Fatty acids
  3. Proteins
  4. Alcohol
  5. Ketone Bodies
14. Which of the following statements concerning both α-ketoglutarate dehydrogenase complex and the pyruvate dehydrogenase complex is FALSE
  1. They are derived from a common gene or common genes by a process of gene duplication and mutation
  2. They both use an α-keto carboxylic acid as a substrate
  3. They both produce an acyl CoA as a product
  4. They are both in the TCA cycle
  5. They both have a requirement for thiamine pyrophosphate, lipoic acid, CoA, NAD+, and FAD as cofactors
15. The symptoms for pyruvate dehydrogenase complex deficiencies are most apparent in the central nervous system because this complex is necessary for the complete oxidation of _______ and the brain is highly reliant upon ________for energy.
  1. fatty acids,:      fatty acids
  2. amino acids:    amino acids
  3. glucose;            glucose
  4. fatty acids;        ketone bodies
  5. alcohol;            acetaldehyde
16. When a brain cell uses energy, all of the following events occur EXCEPT
  1. The ATP to ADP ratio decreases
  2. The NADH to NAD+ ration decreases
  3. The concentration of Acetyl CoA decreases
  4. Increased NADH, ATP, and Acetyl CoA inhibit the pyruvate dehydrogenase complex
  5. More pyruvate is converted to acetylCoA
17. When a muscle cell contracts, all of the following will increase the activity of the pyruvate dehydrogenase complex EXCEPT
  1. Increased oxidation of alcohol
  2. Increased Ca++
  3. Decreased Acetyl CoA
  4. Decreased NADH
  5. Decreased ATP
18. In the mitochondria, there is an efflux of intermediates of the TCA cycle for all of the following reasons EXCEPT
  1. Amino acid synthesis
  2. Neurotransmitter synthesis
  3. Heme synthesis
  4. Gluconeogenesis
  5. Thiamine synthesis
19. TCA cycle intermediates are always being removed for various reasons but the cycle does not run out of intermediates and stop.  This is because we can always make intermediates
  1. From acetyl CoA
  2. From even chain fatty acids
  3. Using anaplerotic reactions
  4. From the catabolism of heme in the spleen
  5. Using the pyruvate dehydrogenase complex and citrate synthase reactions
20. Concerning the anaplerotic enzyme reaction that links glycolysis to the TCA cycle, all of the following are true EXCEPT
  1. The enzyme is pyruvate dehydrogenase located in the mitochondria
  2. The enzyme uses the cofactor biotin
  3. The enzyme becomes more active as the concentration of acetyl CoA increases
  4. The enzyme uses CO2 and ATP as substrates
  5. The enzyme produces oxaloacetate as a product
21. The symptoms for pyruvate carboxylase deficiency are most apparent in the central nervous system because the CNS
  1. Is highly reliant upon the complete oxidation of glucose
  2. Is highly reliant upon the complete oxidation of fatty acids
  3. Cannot run anaplerotic reactions
  4. Does not have mitochondria
  5. Always has very high levels of NADH and ATP
22. Two types of compounds that can be used for anaplerotic reactions are
  1. Acetyl CoA and amino acids
  2. Acetyl Co A and Odd chain fatty acids
  3. Even chain fatty acids and amino acids
  4. Odd chain fatty acids and amino acids
  5. TCA cycle intermediates and amino acids
23. Your patient, Otto Shape, asks you if succinate can be oxidized without using oxygen.  You might use all of the following in your explanation EXCEPT
  1. To oxidize succinate you must use FAD as a substrate
  2. FAD must feed electrons into the electron transport system
  3. In the absence of oxygen, FADH2 cannot be oxidized
  4. If you cannot oxidize FADH2, you will run out of substrate for succinate dehydrogenase
  5. If succinate dehydrogenase is inhibited, the entire TCA cycle would be inhibited and it is our major source of energy
24. When a person starts to run, you can assume that in her leg muscle cells

  1. ADP will increase and inhibit pyruvate dehydrogenase
  2. NADH will increase and activate pyruvate dehydrogenase
  3. Acetyl CoA will increase and activate pyruvate dehydrogenase
  4. NADH will decrease and the TCA cycle will be activated
  5. AMP will increase and inhibit pyruvate dehydrogenase
25. When a person is running, the concentration of Ca++ will increase and bind to allosteric sites on 

  1. Succinate thiokinase and pyruvate dehydrogenase
  2. Succinate thiokinase, pyruvate dehydrogenase and fumarase
  3. Succinate thiokinase, isocitrate dehydrogenase and fumarase
  4. Pyruvate dehydrogenase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase
  5. Isocitrate dehydrogenase, fumarase, malate dehydrogenase, and citrate synthase
26. Otto Shape is a patient that led a sedentary lifestyle but began exercising on a regular basis.  Compared to 6 months ago 
  1. A smaller proportion of glucose is converted to Acetyl CoA when he exercises
  2. Much less oxygen can be delivered to muscle tissue
  3. A larger proportion of glucose is converted to lactate when he exercises
  4. There is a greater ability to oxidize acetyl CoA
  5. There are less TCA enzymes
27. You have a patient who may have developed subclinical deficiencies of many vitamins. To be sure that the pyruvate dehydrogenase and the pyruvate carboxylase reactions would have an adequate amount of cofactors, you would prescribe all of the following EXCEPT 
  1. Biotin
  2. ascorbic acid
  3. Pantothenate
  4. Riboflavin
  5. Thiamine
28. Your patient has arrived in the emergency room with alcohol-related neurological and cardiac ailments.  The lady that brought him in says that he has been on a binge for over a week.  You would guess that some of his problems may be do to
  1. Thiamine deficiency due to inhibition of uptake in the intestine
  2. B12 deficiency due to excess urination
  3. Vitamin E deficiency due to excess urination
  4. Biotin deficiency due to excess sweating
  5. Niacin deficiency due to the destruction of NADH by the alcohol dehydrogenase reaction
29. Your patient is an alcoholic with a buildup of a-ketoacids and symptoms of wet beriberi.   All of the following might be part of a scenario that would explain why peripheral vessels dilate and cardiac muscles loose their contractility EXCEPT
  1. Muscle needs ATP to contract
  2. Most ATP is produced by oxidative phosphorylation
  3. NADH and FADH2 are produced by the TCA cycle
  4. The TCA cycle needs thiamine pyrophosphate to function
  5. A shortage of thiamine results in the inability to oxidize NADH

Answers:

1. Answer: E. Chapter 20, Objective 1: To understand or describe any pathway or cycle, start with the following paradigm for the TCA cycle: Names: Functions: Substrates: Products: Control Enzymes: Regulation: Compartment(s): Tissues of interest Back to question 1.
2. Answer: C. Chapter 20, Objective 2: Name the four dehydrogenase enzymes of the TCA cycle. What are the substrates and products of each reaction? Back to question 2.
3. Answer: C. Chapter 20, Objective 3: What is the approximate energy yield from the oxidation of one acetyl CoA molecule? Back to question 3.
4. Answer: C. Chapter 20, Objective 4: Name the enzyme of the TCA cycle that catalyzes a substrate level phosphorylation. Back to question 4.
5. Answer: E. Chapter 20, Objective 5: What is the difference between a substrate level phosphorylation and oxidative phosphorylation? Back to question 5.
6. Answer: C. Chapter 20, Objective 6: Compare NADH and FADH with respect to: (1) Mechanism of accepting or donating electrons, (2) Affinity for the apoenzyme, (3) reactivity in solution, and (4) ability to act as a feedback inhibitor or activator. Back to question 6.
7. Answer: E. Chapter 20, Objective 7: What is the purpose of the thioester bond in acetyl CoA and succinyl CoA? Back to question 7.
8. Answer: B. Chapter 20, Objective 8: Name the five cofactors of the a-ketoglutarate dehydrogenase reaction. Name the vitamins from which four of them are derived! What is the advantage of a multienzyme complex? Back to question 8.
9. Answer: E. Chapter 20, Objective 10: Several enzyme reactions in the TCA cycle are considered irreversible. Why? Back to question 9.
10. Answer: E. Chapter 20, Objective 9: Given the delta-G0! for each enzymatic step in a sequence of enzymatic reactions, be able to state the delta-G0! for the overall reaction. Back to question 10.
11. Answer: D. Chapter 20, Objective 11: How is the rate of the TCA cycle linked to muscle contraction and the utilization of ATP? Back to question 11.
12. Answer: B. Chapter 20, Objective 12: Name two control enzymes of the TCA cycle. Back to question 12.
13. Answer: E. Chapter 20, Objective 13: Name four dietary sources of acetyl CoA! Back to question 13.
14. Answer: D. Chapter 20, Objective 14: Which enzyme reaction in the TCA cycle is similar to the pyruvate dehydrogenase reaction? How could this relationship come about? Back to question 14.
15. Answer: C. Chapter 20, Objective 15: Why are the symptoms for pyruvate dehydrogenase complex deficiency so apparent in the central nervous system and not in most other tissues? Back to question 15.
16. Answer: D. Chapter 20, Objective 16: Explain how the rate of the pyruvate dehydrogenase complex is related to the rate of utilization of ATP. Back to question 16.
17. Answer: A. Chapter 20, Objective 17: Explain how muscle contraction is related to the rate of the pyruvate dehydrogenase reaction. Back to question 17.
18. Answer: E. Chapter 20, Objective 18: Name five pathways which use TCA cycle intermediates as substrates. What is the effect of these pathways on the TCA cycle? Back to question 18.
19. Answer: C. Chapter 20, Objective 19: If TCA cycle intermediates are constantly being removed for biosynthesis, why doesn't the cycle stop? Back to question 19.
20. Answer: A. Chapter 20, Objectives 20: Be able to fully describe the anaplerotic reaction that links glycolysis and the TCA cycle. Name the enzyme, substrate, product, biological compartment and tissues of interest. Name the regulatory factor (activator) and explain how the system regulates the production of the TCA cycle intermediate. What coenzyme is used in the reaction? Back to question 20.
21. Answer: A. Chapter 20, Objectives 21: Why are the symptoms for pyruvate carboxylase deficiency so apparent in the central nervous system and not in most other tissues? Back to question 21.
22. Answer: D. Chapter 20, Objective 22: In addition to pyruvate, name two other classes of compounds that can be used to as substrates for anaplerotic reactions. Back to question 22.
23. Answer: B. Chapter 20, Objective 23: Concerning Otto Shape, can succinate be oxidized without oxygen being consumed? Back to question 23.
24. Answer: D. Chapter 20, Objective 24: Concerning Otto Shape, explain the effect of increased muscle contraction upon the concentrations of ATP, ADP, AMP, NADH, FAD(2H), and Acetyl Co A. What effect does this have upon the rate of the TCA cycle and the pyruvate dehydrogenase reaction? Back to question 24.
25. Answer: D. Chapter 20, Objective 25: Concerning Otto Shape, what effect does the increased calcium ion concentration in a contracting muscle have upon the rate of the TCA cycle and the pyruvate dehydrogenase reaction? Back to question 25.
26. Answer: D. Chapter 20, Objective 26: Concerning Otto Shape, most of the pyruvate produced during exercise was either oxidized to acetyl CoA or reduced to lactate. Why did training increase the amount of pyruvate being oxidized? Back to question 26.
27. Answer: B. Chapter 20, Objective 27: Concerning a patient who suffers from anorexia nervosa and may have developed subclinical deficiencies of many vitamins, which vitamins would you prescribe to be positive that the pyruvate dehydrogenase and the pyruvate carboxylase reactions would have an adequate amount of cofactors? Back to question 27.
28. Answer: A. Chapter 20, Objective 29: Concerning Al Martini who is an alcoholic, why does he have a thiamine deficiency? Back to question 28.
29. Answer: E. Chapter 20, Objective 28:Concerning Al Martini: Given that a-ketoacids build up in the heart in wet beriberi, develop a scenario that would explain why peripheral vessels dilate and cardiac muscles loose their contractility. Back to question 29.