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Glycogen b.Name the main enzyme of glycogenolysis and explain its function. c.Write the scheme of glucagon action (=signaling pathway) resulting in activation of thisenzyme?
The main enzyme of glycogenolysis is glycogen phosphorylase.
Glycogenolysis is the step-wise removal of glucose units from glycogen to form glucose-6-phosphate.
There are two steps in the process.
1. ##("glycogen")_n + P_i stackrelcolor(blue)("glycogen phosphorylase"color(white)(Xl))(→) ("glycogen")_(n-1) + "glucose-1-phosphate"##
2. ##"glucose-1-phosphate"color(white)(l)stackrelcolor(blue)("phosphoglucomutase"color(white)(Xl))(→) "glucose-6-phosphate"##
Glycogenolysis plays an important role in the fight-or-flight response and in the regulation of glucose levels in the blood.
The Signalling Pathway
The signalling pathway consists of several steps.
1. The pancreas secretes glucagon when the blood sugar is low.
2. Glucagon activates receptors in the cytoplasmic membrane.
3. The receptors activate adenylate cyclase.
4. The adenylate cyclase converts ATP to cyclic AMP (cAMP).
5. cAMP binds to and activates protein kinase A (PKA).
6. PKA activates phosphorylase kinase.
7. Phosphorylase kinase activates glycogen phosphorylase.
8. Glycogen phosphorylase activates glycogenolysis.