Glycogen Metabolism

Question 1

Def of glycogenesis

Answer 1

Process of glycogen formation from glucose

Question 2

Location of glycogenesis

Answer 2

Cytosol of liver and muscles

Question 3

Importance of glycogenesis

Answer 3

Storage of excess glucose to use it later at time of requirement

Question 4

Steps of glycogenesis

Answer 4

Glycogen synthase is the rate limiting enzyme

Question 5

Def of glycogenolysis

Answer 5

Breakdown of glycogen into glucose in liver during fasting and G6p in muscles during exercise

Question 6

Steps of glycogenolysis

Answer 6

Glycogen phophorylase is the rate limiting enzyme

Question 7

Regulation of glycogenolysis and glycogenesis

Answer 7

Because of the importance of maintaining blood glucose levels, the synthesis and degra-
dation of its glycogen storage form are tightly regulated.
In the liver, glycogenesis accelerates during well fed state
whereas glycogenolysis accelerates during fasting. In skeletal muscle, gly-
cogenolysis occurs during active exercise, and glycogenesis begins at rest.
Regulation of glycogen synthesis and degradation is accomplished on two levels.

First, glycogen synthase and glycogen phosphorylase are hormonally regulated to
meet the needs of the body as a whole (Covalent modification).
Second, the pathways of glycogen synthesis and degradation are allosterically con-
trolled to meet the needs of a particular tissue. (Allosteric modification).

Glycogen synthase is activated by insulin ( glut 2) in liver
Inhibited by epinephrine and glucagon

It is activated in muscle by insulin ( glut 4) and inhibited by epinephrine

Glycogen phosphorylase is activated in liver by epinephrine and glucagon and inhibited by insulin

It is activated in muscle by epinephrine ca and AMP and inhibited by insulin and ATP

Question 8

Glycogen storage disease

Answer 8

It is genetic characteristized by accumulation of glycogen

1- von gierke : deficiency in glucose 6 phosphatase results in severe hypoglycemia , lactic acidosis, hepatomegaly , hyperlipidimia, hyper uracimia and doll like facies

2- mcardle : deficiency in muscle glycogen phosphorylase results in cramps and weakness in muscle

3- hers : deficiency in hepatic glycogen phosphorylase results in fasting hypoglycemia , hepatomegaly and cirrhosis

Question 9

Substrate for glycogenesis

Answer 9

1, In liver:
• Blood glucose.
• Other hexoses: fructose and galactose.
• Non-carbohydrate sources: glycerol and lactate. These are
converted first to glucose, then to glycogen.

2. In muscles: Blood glucose only.