Chapter 15 Answers

Glycogen Metabolism and Gluconeogenesis

Book study exercises 4,5 and 8

1) An increase in cAMP will likely lead to:

1. an increase in glycogen formation
2. a decrease in glycogen formation
3. will not have an affect on glycogen metabolism
4. decreases the phosphorylation state of both glycogen phosphorylase and glycogen synthase

For each of the following answer as

2) Glycogen is stored in muscle and liver

3) Glycogen is a major source of stored energy in brain

4) Glycogen fills the nucleus of the cells that store glycogen

5) Glycogen storage occurs in the form of dense granules in the cytosol of cells

6) Why is it important to have different pathways for glycogenesis and glycogenolysis in liver and muscle cells?

7) Which of the following statements about hormonal regulation of glycogen synthesis and degradation are correct?

1. insulin increases the capacity of the liver to synthesize glycogen
2. insulin is secreated in response to low levels of blood glucose
3. glucagon and epinephrine have opposing effects on glycogen metabolism
4. glucagon stimulates the breakdown of glycogen, particularly in the liver
5. the effects of all three of the regulating hormones are mediated by cAMP

9) Write out each of the 3 steps that differ between glycolysis and gluconeogenesis.

10) Pyruvate carboxylase adds a CO₂ at the cost of 1 ATP, yet the same CO₂ is removed later. Why? What is the product of this reaction.

11) Describe the conversion of lactate to PEP. Why not just convert lactate to pyruvate and then reverse the reaction as in the paired reactions of fructose 1,6 bisphosphatase and phosphofructokinase? (hint see the last answer)

12) The presence of epinephrine results in the stimulation of PFK-2 in heart muscle. How does epi affect glycolysis in this organ?

13) How many high energy bonds are required to convert oxaloacetate to glucose?

14) Biotin is a carrier of

1. CO₂
2. two carbon groups
3. three carbon groups
4. acetyl groups

15) Fructose 2,6-bisphosphate is a potent activator of the liver phosphofructokinase and a potent inhibitor of the fructose 2,6-bisphosphatase enzyme. Fructose 2,6-bisphosphate is produced and metabolized by the same bifunctional enzyme phosphofructo kinase 2 (PFK2).

1. Under what conditions would the kinase activities of PFK2 be active?
2. Under what conditions would the phosphatase activities of PFK2 be active?
3. cAMP dependent phosphorylation of PFK2 not only inhibits the kinase but activates the phosphatase.

Under these conditions, gluconeogenesis is sufficiently rapid to meet cellular demand. Explain.

16) Which of the following statements correctly describe what happens when acetyl CoA is abundant?

1. pyruvate carboxylase is activated
2. phosphoenolpyruvate carboxykinase is activated
3. phosphofructokinase is activated
4. if ATP levels are high, oxaloacetate is diverted to gluconeogenesis
5. if ATP levels are low, oxaloacetate is diverted to gluconeogenesis

17) Explain how the enzymatic activity of phosphoenolpyruvate carboxykinase (PEPCK) is allosterically regulated by hormones.

18) Indicate how of the conditions effect gluconeogenesis.

1. increased ATP
2. increases in F 2,6 bisphosphate
3. increases in acetyl CoA
4. starvation
5. high glucose

19) Which of the following hormones bind to the alpha adrenergic receptor

1. epinepherine
2. norepinepherine
3. insulin
4. glucagon
5. cAMP

20) All of the following are gluconeogenic enzymes except:

1. glucose 6-phosphatase
2. fructose 1,6 bisphosphatase
3. phosphoenolpyruvate carboxykinase
4. pyruvate dehydrogenase
5. pyruvate carboxylase

21. Why can’t gluconeogenesis just reverse the actions of pyruvate kinase by coupling the reaction with ATP?