MCAT Biochemistry Practice Test 9: Carbohydrate Metabolism I: Glycolysis, Glycogen, Gluconeogenesis, and the Pentose Phosphate Path

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1. A man collapses while running a marathon and is taken to the emergency room. His blood is found to be somewhat acidic, and further tests show increased lactate dehydrogenase activity. This enzyme is involved in which of the following pathways?

  • A. Anaerobic glycolysis
  • B. β-Oxidation of fatty acids
  • C. Citric acid cycle
  • D. Pentose phosphate pathway

2. Which of the following organs does NOT require a constant supply of glucose from the blood for energy during a fast?

  • A. Red blood cells
  • B. Brain
  • C. Pancreas
  • D. Liver

3. When insulin is released, it acts to increase the absorption of glucose into skeletal muscle predominantly through which of the following transporters?

  • A. GLUT 1
  • B. GLUT 2
  • C. GLUT 3
  • D. GLUT 4

4. After an overnight fast, which of the following enzymes would be expected to have little, if any, physiological activity?

  • A. Malate dehydrogenase
  • B. Glucokinase
  • C. α-Ketoglutarate dehydrogenase
  • D. Phosphofructokinase-1

5. The diagram below shows the effects of arsenic on the metabolism of glyceraldehyde 3-phosphate. As a result, in the presence of arsenic, how many molecules of ATP would be created directly from the conversion of two glucose molecules to four pyruvate molecules?

  • A. 0
  • B. 1
  • C. 2
  • D. 4

6. When fatty acid β-oxidation predominates in the liver, mitochondrial pyruvate is most likely to be:

  • A. carboxylated to phosphoenolpyruvate for entry into gluconeogenesis.
  • B. oxidatively decarboxylated to acetyl-CoA for oxidation in the citric acid cycle.
  • C. carboxylated to oxaloacetate for entry into gluconeogenesis.
  • D. reduced to lactate in the process of fermentation.

7. A biopsy is done on a child with an enlarged liver and shows accumulation of glycogen granules with single glucose residues remaining at the branch points near the periphery of the granule. The most likely genetic defect is in the gene encoding:

  • A. α-1,4 phosphorylase (glycogen phosphorylase).
  • B. α-1,4:α-1,6 transferase (branching enzyme).
  • C. α-1,4:α-1,4 transferase (part of debranching enzyme complex).
  • D. α-1,6 glucosidase (part of debranching enzyme complex).

8. An investigator is measuring the activity of various enzymes involved in reactions of intermediary metabolism. One of the enzymes has greatly decreased activity compared to reference values. The buffer of the assay contains citrate. Which of the following enzymes will most likely be directly affected by the use of citrate?

  • A. Fructose-2,6-bisphosphatase
  • B. Isocitrate dehydrogenase
  • C. Phosphofructokinase-1
  • D. Pyruvate carboxylase

9. After a brief period of intense exercise, the activity of muscle pyruvate dehydrogenase is greatly increased. This increased activity is most likely due to:

  • A. decreased ADP.
  • B. increased acetyl-CoA.
  • C. increased NADH/NAD+ ratio.
  • D. increased pyruvate concentration.

10. After a large, well-balanced meal, all of the following substances would be expected to be elevated EXCEPT:

  • A. fatty acids.
  • B. insulin.
  • C. glucose.
  • D. glucagon.

11. A man is given antibiotics to treat a urinary tract infection and develops an episode of red blood cell lysis. Further studies show weakness of the plasma membrane and Heinz bodies (collections of oxidized hemoglobin). Which of the following enzymes is most likely defective in this patient?

  • A. Fructose-1,6-bisphosphatase
  • B. Glucose-6-phosphate dehydrogenase
  • C. Hexokinase
  • D. Pyruvate kinase

12. The unique enzymes of gluconeogenesis are used to circumvent specific irreversible steps of glycolysis. Which of the following correctly pairs an enzyme from glycolysis with its corresponding enzyme(s) used in gluconeogenesis?

  • A. Phosphofructokinase-1 / fructose-1,6-bisphosphatase
  • B. Pyruvate dehydrogenase / pyruvate carboxylase and phosphoenolpyruvate carboxykinase
  • C. Hexokinase / glucokinase
  • D. Pyruvate kinase / glucose-6-phosphatase

13. After an overnight fast, which of the following processes would be expected to occur at an elevated rate compared with the well-fed state?

  • A. Glycolysis
  • B. Glycogenolysis
  • C. Glycogenesis
  • D. Glycerol synthesis

14. Which of the following is/are function(s) of NADPH in the cell?

I. Antimicrobial resistance via bacterial destruction by bleach within lysosomes.

II. Involvement in the production of the precursors to steroid hormones.

III. Functional carriage of energy across organelle membranes for use within the mitochondria

  • A. I only
  • B. I and II only
  • C. II and III only
  • D. I, II, and III

15. Each of the following catalyzes a rate-limiting step of a carbohydrate metabolism pathway EXCEPT:

  • A. hexokinase.
  • B. glycogen synthase.
  • C. glucose-6-phosphate dehydrogenase.
  • D. fructose-1,6-bisphosphatase.