Glycogenolysis Regulation
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Biochemistry › Glycogenolysis Regulation
Which of the following statements about glycogen phosphorylase (GP) is incorrect?
AMP is an inhibitor of glycogen phosphorylase.
Glucose-6-phosphate is a negative regulator of glycogen phosphorylase.
The dephosphorylated form of glycogen phosphorylase is less active.
Glucose is a competitive inhibitor of glycogen phosphorylase.
This enzyme is active during times of starvation.
Explanation
AMP is an activator of GP, whereas ATP is an inhibitor of GP. GP cleaves the alpha 1-4 glycosidic bond between a terminal glucose molecule and the rest of the glycogen straight chain, yielding glucose-1-phosphate during glycogenolysis.
The process of glycogenolysis is an example of __________.
Phosphorolysis
Hydrolysis
Thiolysis
Phosphorylation
Lysis
Explanation
Phosphorolysis is the name given to the addition of phosphate across a bond. Remember that in glycogenolysis, glycogen phosphorylase adds a phosphate across the a-1,4-glycosidic bonds between the glucose units of glycogen. The result is that glucose leaves as glucose-1-phosphate. If hydrolysis were performed instead of phosphorolysis, free glucose would be severed from glycogen and would be able to leave the cell.
Phosphorylation of glycogen phosphorylase has what effect on the enzyme?
Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A
Inactivation, conversion from glycogen phosphorylase B to glycogen phosphorylase A
Activation, conversion from glycogen phosphorylase A to glycogen phosphorylase B
Phosphorylation has no effect
Phosphorylation only confers partial activation
Explanation
Phosphorylation of glycogen phosphorylase activates it, converting it from its inactive B-form to its active A-form.