Problem 1
Match the terms on the left with the descriptions on the right. (a) UDP-glucose _____ (b) UDP-glucose pyrophosphorylase _____ (c) Glycogen synthase _____ (d) Glycogenin _____ (e) Branching enzyme _____ (f) Glucose 6 -phosphate _____ (g) Glycogen synthase kinase _____ (h) Protein phosphatase 1 _____ (i) Insulin _____ (j) Glycogen phosphorylase \(a\) _____ 1\. Glucose 1 -phosphate is one of its substrates. 2\. Potent activator of glycogen synthase \(b\) 3\. Glucose sensor in the liver. 4\. Activated substrate for glycogen synthesis. 5\. Synthesizes \(\alpha-1,4\) linkages between glucose molecules. 6\. Leads to the inactivation of glycogen synthase kinase. 7\. Synthesizes \(\alpha-1,6\) linkages between glucose molecules. 8\. Catalyzes the formation of glycogen synthase \(b\). 9\. Catalyzes the formation of glycogen synthase \(a\). 10\. Synthesizes the primer for glycogen synthesis.
Problem 2
What enzymes are required for the synthesis of a glycogen particle starting from glucose 6 -phosphate?
Problem 3
UDP-glucose is the activated precursor for glycogen synthesis, but ultimately ATP is the power behind glycogen synthesis. Prove it by showing the reactions required to convert glucose 6 -phosphate into a unit of glycogen with the concomitant regeneration of UTP.
Problem 4
The following reaction accounts for the synthesis of UDP-glucose. This reaction is readily reversible. How is it made irreversible in vivo? $$\text { Glucose 1-phosphate }+\text { UTP } \rightleftharpoons \text { UDP-glucose }+\mathrm{PP}_{\mathrm{i}}$$
Problem 5
Why does activation of the phosphorylated \(b\) form of glycogen synthase by high concentrations of glucose 6 -phosphate make good biochemical sense?
Problem 6
Describe the separate roles of glycogenin and glycogen synthase in glycogen synthesis.
Problem 7
The complete oxidation of glucose 6 -phosphate derived from free glucose yields 30 molecules ATP, whereas the complete oxidation of glucose 6-phosphate derived from glycogen yields 31 molecules of ATP. Account for this difference.
Problem 8
Phosphoglucomutase is crucial for glycogen breakdown as well as for glycogen synthesis. Explain the role of this enzyme in each of the two processes.
Problem 9
Write a balanced equation showing the effect of the simultaneous activation of glycogen phosphorylase and glycogen synthase. Include the reactions catalyzed by phosphoglucomutase and UDP-glucose pyrophosphorylase.
Problem 12
Suggest an explanation for the fact that the amount of glycogen in type I glycogen-storage disease (von Gierke disease) is increased.
