BIOCHEMISTRY 4613/6613

Exam 2 - February 17, 1999

Row number: Name:

Multiple choice ( 2 points each):

1. Lactose intolerance involves:

(a) the inability to metabolize fructose

(b) the inability to metabolize galactose

(c) the lack of the intestinal enzyme sucrase

(d) the lack of the intestinal enzyme lactase

2. The main function of the pentose shunt is to:

(a) supply energy

(b) give the cell a back-up capability should glycolysis fail

(c) provide energy and reducing power

(d) provide pentoses and NADPH

3. The hormone that is secreated during hypoglycemia which stimulates the liver to release glucose into the blood is

(a) epinephrine

(b) glucagon

(c) insulin

(d) glycogenin

4. Galactosemia is a genetic disease associated with the inability to metabolize

(a) glucose

(b) fructose

(c) lactose

(d) galactose

5. A coenzyme form of pantothenic acid is

(a) lipoic acid

(b) coenzyme A

(c) TPP

(d) NADPH

6. The coenzyme TPP is required by reactions involving:

(a) hydrogen transfer

(b) generation of acyl groups

(c) decarboxylation

(d) CO₂ fixation

7. The coenzyme lipoic acid is required by reactions involving:

(a) hydrogen transfer

(b) generation of acyl groups

(c) hydrogen transfer

(d) CO₂ fixation

8. Coenzyme A is required by reactions involving:

(a) acyl group transfer

(b) generation of acyl groups

(c) hydrogen transfer

(d) decarboxylation

9. The coenzyme biotin is required by reactions involving:

(a) acyl group transfer

(b) decarboxylation

(c) CO₂ fixation

(d) generation of acyl groups

10. Avidin binds with and prevents the absorption of the following vitamin from the gut tract:

(a) thiamin

(b) biotin

(c) pantothenic acid

(d) lipoic acid

11. What TCA cycle intermediate helps regulate the rate of glycolysis by directly influencing the activity of phosphofructokinase?

(a) citrate

(b) isocitrate

(c) succinate

(d) oxaloacetate

12. What is the net ATP yield (from both substrate level and oxidative phosphorylation) for the conversion of one molecule of pyruvate to CO₂ and H₂O via the TCA cycle?

(a) 12

(b) 15

(c) 24

(d) 30

13. What is the net ATP yield (from both substrate level and oxidative phosphorylation) for the conversion of one molecule of acetyl CoA to CO₂ and H₂O via the TCA cycle?

(a) 12

(b) 15

(c) 24

(d) 30

14. How many CO₂'s are produced during one turn of the TCA cycle?

(a) 0

(b) 1

(c) 2

(d) 4

15. How many FADH₂'s are produced during one turn of the TCA cycle?

(a) 0

(b) 1

(c) 2

(d) 4

16. How many NADPH's are produced during the conversion of one molecule of acetyl CoA to CO₂ and H₂O via the TCA cycle?

(a) 0

(b) 1

(c) 2

(d) 3

17. How many ATP's are used during one turn of the TCA cycle?

(a) 0

(b) 1

(c) 2

(d) 4

18. The carbons from propionic acid enter the TCA cycle as:

(a) acetyl CoA

(b) -ketoglutarate

(c) succinyl CoA

(d) oxaloacetate

19. An example of gluconeogenesis is:

(a) conversion of lactic acid to glucose

(b) conversion of glycogen to glucose

(c) conversion of glucose to glycogen

(d) conversion of glucose to ribose 5 phosphate

20. The function of the TCA cycle is characterized by all of the following statements EXCEPT

(a) it generates NADH and FADH₂

(b) it generates GTP

(c) it catalyzes the complete oxidation of acetyl CoA to CO₂ and H₂O

(d) it provides for the net synthesis of oxaloacetate from acetyl CoA

21. Which of the following enzymes is NOT involved in the conversion of lactate to glucose?

(a) glucose 6 phosphatase

(b) phosphofructokinase

(c) pyruvate carboxylase

(d) PEP carboxykinase

22. Glucagon promotes glycogenolysis (breakdown of glycogen) by stimulating the synthesis of:

(a) cyclic AMP

(b) ATP

(c) 5'-AMP

(d) glucose 6 phosphate

23. Why does glucose from liver glycogen enter the blood but not from muscle glycogen?

(a) glucose cannot move out of a muscle

(b) free glucose is used up very rapidly in muscle cells

(c) muscle cells do not have phosphoglucomutase

(d) muscle cells do not have glucose 6 phosphatase

24. Which of the following metabolic processes would be the most affected in vitamin B-12 deficiency?

(a) glycolysis

(b) acetyl CoA metabolism

(c) propionic acid metabolism

(d) the TCA cycle

25. Epinephrine triggers an increased rate of glycogen breakdown in muscle by stimulating:

(a) the activation of hexokinase

(b) the activation of glyceraldehyde 3 phosphate dehydrogenase

(c) the conversion of glycogen phosphorylase b to glycogen phosphorylase a

(d) the activation of pyruvate kinase

26. The activated form of glucose for glycogen synthesis is:

(a) glucose 1 phosphate

(b) glucose 6 phosphate

(c) glucose 1,6 bisphosphate

(d) UDP-glucose

27. The glycogen-branching enzyme catalyzes:

(a) formation of 1-4 linkages during glycogen synthesis

(b) formation of 1-4 linkages during glycogen synthesis

(c) formation of 1-6 linkages during glycogen synthesis

(d) formation of 1-6 linkages during glycogen synthesis

28. Which of the following is NOT required for the oxidative decarboxylation of pyruvate to form acetyl CoA?

(a) NAD⁺

(b) lipoic acid

(c) ATP

(d) FAD

29. Which of the following is an allosteric inhibitor of pyruvate dehydrogenase?

(a) glucose 6 phosphate

(b) acetyl CoA

(c) pyruvate

(d) ADP

30. Which of the following is an allosteric inhibitor of isocitrate dehydrogenase:

(a) acetyl CoA

(b) citrate

(c) ADP

(d) ATP

31. Which is the most effective in inhibiting the TCA cycle?

(a) a high ratio of NAD/NADH

(b) a high ratio of NADH/NAD

(c) a high ratio of NADH/FADH₂

(d) a high ratio of NADH/NADPH

32. The glyoxylate cycle, in conjunction with the TCA cycle, accomplishes the:

(a) net conversion of lipid to carbohydrate

(b) complete oxidation of acetyl CoA to CO₂ plus reduced coenzymes

(c) allows for the complete oxidation of glucose

(d) produces NADPH and pentoses

33. Which of the following pathways is stimulated by epinephrine?

(a) pentose shunt

(b) glycolysis

(c) gluconeogenesis

(d) TCA cycle

34. Which of the following compounds CANNOT serve as the starting material for the synthesis of glucose via gluconeogenesis in animals?

(a) -ketoglutarate

(b) lactate

(c) pyruvate

(d) acetyl CoA

35. Which of the following is an allosteric inhibitor of phosphofructokinase?

(a) glucose 6 phosphate

(b) citrate

(c) fructose 2,6 bisphosphate

(d) ATP

36. What is the net ATP yield (from both substrate level and oxidative phosphorylation) for the conversion of one free glucose molecule to CO₂ and H₂O via glycolysis and the TCA cycle?

(a) 12

(b) 15

(c) 38

(d) 39

37. Oxaloacetate moves through the mitochondrial membrane

(a) by passive diffusion

(b) after conversion to pyruvate

(c) after conversion to malate

(d) after conversion to fumarate

38. The enzyme involved in the conversion of fructose 1,6 bisphosphate to fructose 6 phosphate is

(a) phosphofructokinase

(b) fructokinase

(c) fructose 6 phosphatase

(d) fructose 1,6 bisphosphatase

39. Gluconeogenesis occurs in

(a) all tissues

(b) muscle tissue

(c) liver tissue

(d) nerve tissue

Short answer: USE NAME REACTIONS - NO STRUCTURES REQUIRED

1. Illustrate the Cori cycle and briefly describe its importance. (6 points)

2. Give an example of an enzymatic reaction which is under covalent regulation. Name the substrate(s) and product(s) as well as the activators and inhibitors of the enzyme. (6 points)

3. Use name reactions to illustrate how pyruvate can be converted to phosphoenolpyruvate during gluconeogenesis. Name all reactants, products and enzymes involved. (10 points)