1.) What are the circumstances under which glycogen would be broken downto its c

Question

1.) What are the circumstances under which glycogen would be broken downto its component glucose molecules?

2.) How are glycogen phosphorylase and glycogen synthase reciprocally controlled?

3.) What is the mechanism by which phosphoprotein inhibitor-1 inhibits phosphoprotein phosphatase-1?

4.)Summarize the HORMONAL CONTROL that regulatesthe metabolism of glycogen?

5.) Why are there different rate limiting steps for gluconeogenesis that glycolysis when, in fact, they are just "reversal" pathways of one another?

Explanation / Answer

1)Break down of glycogen to glucose molecules is called Glycogenolysis.It takes place when glucose level in the blood decreases as in heavy exercise or due to lack of food for more duration.In this process, glycogen which is stored in the liver and muscles first converted to glucose-1-phosphate and then to glucose-6-phosphate sugars.This process is controlled by the harmones glucagon which is released from the pancreatic cells and the epinephrin from the adrenal glands.

2)Glycogen phosphorylase enzyme helps in breaks up glycogen to glucose subunits where as glycogen synthase involved in converting glucose to glycogen.Glycogen phosphorylase and synthase are reciprocally regulated by the harmone-triggered cAMP cascade which is acting through protein kinase A.    Protein kinase A adds a phosphoryl group to glycogrn synthase which leads to a decrease in enzymatic activity.It prevents glycigen from being synthesized at the same time being breakdown.                      

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