2) Is the energy required to synthesize glycogen from glucose 6-phosphate the same as the energy required to degrade glycogen to glucose 6-phosphate?

3) The phosphorolityc cleavage of glycogen is key for glycogen metabolism. Why?

4) T/F

• glycogen is stored in muscle and liver
• glycogen is a major source of stored energy in brain
• glycogen reserves can exceed the equivalent of 10,000 kcal in the average human
• glycogen fills the nucleus of the cells that store glycogen
• glycogen storage occurs in the form of dense granules in the cytosol of cells

5) Which enzyme is not required for the production and release of LARGE amounts of glucose from the liver.

1. glucose 6-phosphatase
1. fructose 1,6-bisphosphatase
1. debranching enzyme
1. phosphoglucosmutase
1. glycogen phosphorylase

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

7) How does the regulation of phosphorylase in the liver differ from the scheme for phosphorylase regulation in muscle shown in figure 23-8 in Stryer?

8) For figure 23-8, determine which forms of the phosphorylase are active and the enzyme that catalyzes the conversion of the phosphorylated/dephosphorylated form of phosphorylase

9) T/F

• glycogen synthase is activated when it is dephosphorylated
• glycogen synthase is activated when it is phosphorylated
• glycogen synthase is activated when it is phosphorylated and in the presence of high levels of glucose 6-phosphate
• glycogen synthase is activated when it is phosphorylated and in the presence of high levels of AMP

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

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

11) An investigator has a sample of purified muscle phosphorylase b that she knows is inactive. Suggest two test tube (invitro) methods that could be used to make the enzyme active. After the phosphorylase is activated, she incubates the enzyme with a sample of unbranched glycogen. However she finds no uncleaved glycosal units. What else is needed for the cleavage of glycosal residues by active phosphorylase?

12) Write out a detailed pathway of the hormonal control of glycogen synthesis and its break down. Be certain to include the allosteric effectors for your pathway.