Week 5: Glycogenolysis

Question 1

What is glycogenolysis

Answer 1

breaking down glycogen

Question 2

Glycogenolysis occurs in what state

Answer 2

fasting state with high glucagon levels

Question 3

Glycogen glycosidic linkages

Answer 3

α-1. 6 branches

α-1, 4 trunks

Question 4

Glycogenolysis in skeletal muscle

Answer 4

Glycogen + Pi -glycogen phosphorylase-> glucose-1-phosphate

glucose-1-phosphate-phosphoglucomutase-> Glucose-6-phosphate

Up to this point the liver and skeletal muscle glycogenolysis is the same

In skeletal muscle the glucose-6-phosphate is sent down the glycolytic pathway

Question 5

Glycogenolysis in the liver

Answer 5

• Glycogen + Pi -glycogen phosphorylase-> glucose-1-phosphate
• glucose-1-phosphate-phosphoglucomutase-> Glucose-6-phosphate
• Up to this point the liver and skeletal muscle glycogenolysis is the same

Livers goal in glycogenolysis is to Restore and maintain glucose in the blood

Glucose-6-phosphate -glucose-6-phosphatase-> glucose + Pi

glucose -GLUT 2-> blood (by facilitated diffusion

Question 6

GLUT 2 regulation

Answer 6

• Low affinity constitutive transporter in RBC and Liver
• Concentration-dependent

Question 7

What signals the muscle to undergo glycogenolysis

Answer 7

• increasing [AMP] binds to glycogen phosphorylase as an allosteric activator + [AMP] activates PFK-1 to activate the glycolytic pathway
• neural innervation triggers release of [Ca2+] and high [Ca2+] activates glycogen phosphorylase kinase which activates glycogen phosphorylase to increase glucose release and phosphorylates glycogen synthase to inhibit glycogenesis by inactivating glycogen synthase preventing a feudal loop
• Epinephrine activates through Gαs activating adenylate cyclase which activates cAMP which activates PKA and this phosphorylates glycogen phosphorylase kinase which phosphorylates glycogen phosphorylase by phosphorylation to activate glycogenolysis and inhibits glycogen synthase by phosphorylation and inhibit glycogenesis
• Glucagon has no effect on skeletal muscle

Question 8

Glucagon effect on liver

Answer 8

glucagon -Gαs-> Adenylate cyclase -+> cAMP -+->PKA -+-> glycogen phosphorylase kinase by phosphorylation which phosphorylates glycogen phosphorylase activating it, and inhibiting glycogen synthase which breaks down glycogen to glucose-6-phosphate

glycogen phosphorylase can now take glycogen to glucose-6-phosphate

Question 9

Epinephrine effect on liver

Answer 9

Epinephrine activates through Gαs activating adenylate cyclase which activates cAMP which activates PKA and this phosphorylates glycogen phosphorylase kinase which phosphorylates glycogen phosphorylase by phosphorylation to activate glycogenolysis and inhibits glycogen synthase by phosphorylation and effectively inhibit glycogenesis

Question 10

Fate of glucose-6-phosphate in the liver in the fasting state

Answer 10

glucose-6-phosphatase -glucose-6-phosphatase-> Glucose + Pi

Glucose -GLUT 2->