Question

How do insulin, adrenaline, and glucagon control glycogen metabolism?

Answer 1

Answer-

1. Glucagon stimulates glycogen breakdown i. e. Glycogenolysis in liver cells when blood glucose level decreases. Pancreas synthesizes glucagon when blood glucose level decreases to increase blood glucose level. Glucagon binds to receptors present on liver and muscle cells, triggers signalling pathway. When glucagon binds with receptor, that increases intracellular cAMP synthesis and cAMP activates protein kinase A. Protein kinase A activates phosphorylase kinase and phosphorylase kinase activates glycogen phosphorylase enzyme that cleaves 14 bond and releases glucose 1-phosphate and then glucose 1-phosphate is converted into glucose 6-phosphate. And then this glucose increases blood glucose level.

2. Epinephrine works similarly as glucagon. Epinephrine also known as adrenaline, it stimulates glycogen breakdown when blood sugar level decreases. Adrenaline binds to adrenergic receptors on muscles specifically and triggers cascade that activates glycogen phosphorylase enzyme that degrades glycogen into glucose.

3. Insulin is peptide hormone which is synthesized by pancreas when blood glucose level increases. Insulin stimulates glycogen synthesis in muscle cells and liver. Insulin binds to the tyrosine kinase receptor on liver and muscle cells and insulin sensitive protein kinase is activated. Active Insulin sensitive protein kinase activates protein phosphatase I and active protein phosphatase I dephosphorylates glycogen synthase. When glycogen synthase dephosphorylated it is activated and active glycogen synthase starts to synthesize glycogen from glucose.