Biochemistry : Glycogenolysis Regulation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Glycogenolysis Regulation

Phosphorylation of glycogen phosphorylase has what effect on the enzyme?

Possible Answers:

Inactivation, conversion from glycogen phosphorylase B to glycogen phosphorylase A

Phosphorylation only confers partial activation

Activation, conversion from glycogen phosphorylase A to glycogen phosphorylase B

Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A

Phosphorylation has no effect

Correct answer:

Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A

Explanation:

Phosphorylation of glycogen phosphorylase activates it, converting it from its inactive B-form to its active A-form. 

Example Question #9 : Alternative Pathways

The process of glycogenolysis is an example of __________.

Possible Answers:

Phosphorylation

Thiolysis

Lysis

Phosphorolysis

Hydrolysis

Correct answer:

Phosphorolysis

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.

Example Question #2 : Glycogenolysis Regulation

Which of the following statements about glycogen phosphorylase (GP) is incorrect?

Possible Answers:

The dephosphorylated form of glycogen phosphorylase is less active.

This enzyme is active during times of starvation.

AMP is an inhibitor of glycogen phosphorylase.

Glucose is a competitive inhibitor of glycogen phosphorylase.

Glucose-6-phosphate is a negative regulator of glycogen phosphorylase.

Correct answer:

AMP is an inhibitor of glycogen phosphorylase.

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.

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