Glycogenolysis

Question 1

Catalyzes phosphorolytic cleavage

Answer 1

Glycogen phosphorylase

Question 2

Stimulates glycogen breakdown in the liver

Answer 2

Glucagon

Question 3

Prepares glucose-1-phosphate for glycolysis

Answer 3

Phosphoglucomutase

Question 4

Liberates a free glucose residue

Answer 4

Alpha-1.6-glucosidase

Question 5

Shifts the location of several glucose residues

Answer 5

Transferase

Question 6

Removal of a glucose residue by the addition of phosphate

Answer 6

Phosphorolysis

Question 7

Review the structure of a glycogen

Answer 7

Strongly branched polymer with linear chains linked by 1,4-bonds and branching formed every 4-8 residues for 1,6-glycosidic bonds
More branches = more non reducing ends ===>more glucose is broken and more energy is made

Question 8

Explain the breakdown of glycogen

Answer 8

An inorganic phosphate cleaves glucose in the linear areas (phosphorylisis)
Glycogen phosphorylase: for cleaving alpha-1,4 linkages to release glucose from the no reducing end. It gets suck in the branching point.
Tranferase: transfers the linear portion back to the main chain. Removes the alpha-1,6-glucose
De branching enzyme: alpha-1,6-glucosidase removes the alpha-1,6-glucose via hydrolysis
*transferase + glucosidase = 1 enzyme in eukaryotes
Glycogen can be broken down into glucose-1-P (90%) by phospholyase from alpha-1,4-linked and glucose (10%) from alpha-1,6-linked from the alpha-1,6-glucosidase
Glucose-1-P + glucose = glucose-6-P by phosphoglucomutase

Question 9

Explain the regulation of glycogen breakdown

Answer 9

Insulin, ATP (muscle), glucose and glucose-6-phosphate (muscle) inhibit glycogen phosphorylase
Epinephrine (exercise), glucagon (hungry), AMP (muscle, breaks down product ATP, Low energy signal) activate glycogen phosphorylase
Low energy —-> glycogenolysis
High energy —> inhibit glycogenolysis

Question 10

Highlight the importance of glycogen metabolism in glucose homeostasis

Answer 10

Insulin turns on glycogenesis and shuts down glycogenolysis
Glucagon activates glycogenolysis, shuts down glycogenesis
Insulin—> insulin receptor (tyrosine kinase receptor)—->PI3K/PKB (inhibit glycogenolysis) —-> increase glucose intake —->promote glycogen synthesis

Glucagon—->glucagon receptor (G protein receptor) —->activate adenylate cyclase ——> produce cyclic AMP —->PKA (inhibits glycogen synthase therefore inhibiting glycogenesis) —-> glycogen phosphorylase —->glycogenolosis

Question 11

Compare and contrast liver glycogen breakdown and muscle glycogen breakdown

Answer 11

Muscle glycogen needs to be used immediately because of the necessity of ATP, the liver transports energy for the rest of the body.
Liver cells distribute energy in the form of glucose muscle cells use power for exercise
Transferase and debranching enzyme and phosphorylase are in the muscle
Phosphogalactomase in the liver
Glucose- 6-phosphate is only present in the liver