Question

1. Following a meal, fructose 2, 6 bisphosphate levels will be elevated in the liver. Under these conditions which of the following will be dephosphorylated and inactive?

a) pryuvate kinase

b) glycogen synthase

c) PFK1

d) glycogen phosphorylase

Other answers have said that the correct answer is glycogen synthase, but this doesn't make sense to me because when glycogen synthase is dephosphorylated it is active rather than inactive? I thought the answer would be glycogen phosphorylate, which would be dephosphorylated and inactive? Other answers on Chegg have said PFK1, so some clarification would be helpful.

2.Which of the following compounds or hormones will not facilitate the process of skeletal muscle glycogenolysis?

A) Epinephrine

B) Glucagen

C) Ca ++

D) AMP:

Other answers have said Ca+, but this also doesn't make sense to me because I thought glucagon does not have any impact on skeletal muscle? Thanks!

Answer 1

Yes you are right In both cases .

1. It is glycogen phosphorylase that is regulated by reversible phosphorylation and become inactive . It is beacuse after a meal the incoming glucose need to be utilised not the stored glucose present in form of glycogen . Glycogen phosphorylase is involved in glycogenolysis as there is no need of glycogenolysis so this enzyme should be inactive .

Fructose 2,6 bisphisphate act as a activator of phosphofructokinase -1 and frcutose 1-6, bisphisphate act as a activator of pyruvate kinase so both of these ezymes will be activated during elevated levels of fructose 2,6 bisphisphate .

2. Glucagon acts only on hepatic glycogenolysis and gluconeogenesis and it does not have any impact on skeletal muscle cells .

Epinephrine do play a role in stimulating glycogenolysis in skeletal muscles .

AMP and Ca++ ions stimulate glucogen degradation by activation of PKA that enhance the conversion of glycogen to glucose 1- phosphate .