MCAT Biochemistry Practice Test 10: Carbohydrate Metabolism II: Aerobic Respiration

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1. During a myocardial infarction, the oxygen supply to an area of the heart is dramatically reduced, forcing the cardiac myocytes to switch to anaerobic metabolism. Under these conditions, which of the following enzymes would be activated by increased levels of intracellular AMP?

  • A. Succinate dehydrogenase
  • B. Phosphofructokinase-1
  • C. Isocitrate dehydrogenase
  • D. Pyruvate dehydrogenase

2. A patient has been exposed to a toxic compound that increases the permeability of mitochondrial membranes to protons. Which of the following metabolic changes would be expected in this patient?

  • A. Increased ATP levels
  • B. Increased oxygen utilization
  • C. Increased ATP synthase activity
  • D. Decreased pyruvate dehydrogenase activity

3. Which of the following INCORRECTLY pairs a metabolic process with its site of occurrence?

  • A. Glycolysis—cytosol
  • B. Citric acid cycle—outer mitochondrial membrane
  • C. ATP phosphorylation—cytosol and mitochondria
  • D. Electron transport chain—inner mitochondrial membrane

4. Which of the following processes has the following net reaction?

2 acetyl-CoA + 6 NAD+ + 2 FAD + 2 GDP + 2 Pi + 6 H2O → 4 CO2 + 6 NADH + 2 FADH2 + 2 GTP + 6 H+ + 2 CoA–SH

  • A. Glycolysis
  • B. Fermentation
  • C. Tricarboxylic acid cycle
  • D. Electron transport chain

5. In glucose degradation under aerobic conditions:

  • A. oxygen is the final electron acceptor.
  • B. oxygen is necessary for all ATP synthesis.
  • C. net water is consumed.
  • D. the proton-motive force is necessary for all ATP synthesis.

6. Fatty acids enter the catabolic pathway in the form of:

  • A. glycerol.
  • B. adipose tissue.
  • C. acetyl-CoA.
  • D. ketone bodies.

7. In which of the following reactions is the reactant oxidized?

  • A. FAD → FADH2
  • B. NAD+ → NADH
  • C. NADPH → NADP+
  • D. ADP → ATP

8. In which part of the cell is cytochrome c located?

  • A. Mitochondrial matrix
  • B. Outer mitochondrial membrane
  • C. Inner mitochondrial membrane
  • D. Cytosol

9. Which of the following correctly shows the amount of ATP produced from the given high-energy carriers?

  • A. FADH2 → 1 ATP
  • B. FADH2 → 1.5 ATP
  • C. NADH → 3 ATP
  • D. NADH → 3.5 ATP

10. Why is it preferable to cleave thioester links rather than typical ester links in aerobic metabolism?

  • A. Oxygen must be conserved for the electron transport chain.
  • B. Thioester hydrolysis has a higher energy yield.
  • C. Typical ester hydrolysis cannot occur in vivo.
  • D. Thioester cleavage requires more energy.

11. Which enzyme converts GDP to GTP?

  • A. Nucleosidediphosphate phosphatase
  • B. Nucleosidediphosphate kinase
  • C. Isocitrate dehydrogenase
  • D. Pyruvate dehydrogenase

12. Which of the following best explains why cytosolic NADH can yield potentially less ATP than mitochondrial NADH?

  • A. Cytosolic NADH always loses energy when transferring electrons.
  • B. Once NADH enters the matrix from the cytosol, it becomes FADH2.
  • C. Electron transfer from cytosol to matrix can take more than one pathway.
  • D. There is an energy cost for bringing cytosolic NADH into the matrix.

13. In high doses, aspirin functions as a mitochondrial uncoupler. How would this affect glycogen stores?

  • A. It causes depletion of glycogen stores.
  • B. It has no effect on glycogen stores.
  • C. It promotes additional storage of glucose as glycogen.
  • D. Its effect on glycogen stores varies from cell to cell.

14. Which complex does not contribute to the proton-motive force?

  • A. Complex I
  • B. Complex II
  • C. Complex III
  • D. Complex IV

15. Which of the following directly provides the energy needed to form ATP in the mitochondrion?

  • A. Electron transfer in the electron transport chain
  • B. An electrochemical proton gradient
  • C. Oxidation of acetyl-CoA
  • D. β-Oxidation of fatty acids