BCH 361 Lecture Notes - Lecture 8: Phosphorylase, Transferase, Glycogen Debranching Enzyme

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9 Nov 2020
BCH 361 Advanced Biochemistry I Fall 2020
Group Discussion Questions
Week 8 (November 2/3)
There is no case study this week. Youve had a lot of assignments due lately and I think we all need a
little breather. Instead we will have some time devoted to a) things that are stressing you out; b) how
you manage your time to avoid getting stressed. Think about what you feel comfortable sharing relating
to these issues.
Additional questions for study or discussion.
1. Predict the mechanism of the enzyme-catalyzed reaction shown below. Explain how the
epoxide can inhibit this enzyme.
2. Glycogen is not as reduced as fatty acids are, and consequently not as energy rich. Why do
animals store any energy as glycogen? Why not convert all excess fuel into fatty acids?
3. α-Amylose is an unbranched polymer of glucose. Why is this polymer not as effective a storage
form of glucose as glycogen?
4. Water is excluded from the active site of glycogen phosphorylase. Predict the effect of a
mutation that allows water to enter the active site.
5. Glycogen debranching enzyme and the transferase activity are found on the same polypeptide.
What advantages are there to having these activities on a single molecule?
6. There must be a way to shut down glycogen degradation once the energy needs have been met
to prevent the wasteful depletion of glycogen. What mechanisms are used to slow down and
stop further glycogen breakdown?
7. In muscle tissue, the rate of conversion of glycogen to glucose-6-phosphate is determined by the
ratio of phosphorylase a (active) to phosphorylase b (less active). Determine what happens to
the rate of glycogen breakdown if a muscle preparation containing glycogen phosphorylase is
treated with (a) phosphorylase b kinase and ATP; (b) phosphorylase a phosphatase; (c)
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