Other Sugar Pathways (Module 3 Lecture 1)

Question 1

What enzymes are needed for glycogenolysis?

Answer 1

1. Glycogen phosphorylase
2. Transferase
3. Alpha 1,6-glycosidase

Question 2

Define glycogenolysis.

Answer 2

Removing glucose (one by one) from glycoen via phosphorylysis NOT hydrolysis.

Question 3

Describe the role of glycogen phosphorylase:

Answer 3

Glycogen (n residues) –> Glucose 1-phosphate + Glycogen (n - 1 residues)

Question 4

Describe the role of transferase during glycogenolysis.

Answer 4

1. After glycogen phosphorylase has reduced branches to 4 linkages,
2. Transferase transfers 3 glycosyl residues to main chain
3. Alpha 1,6-glycosidase releases the remaining glycosyl residue (with the 1,6 attachment) as free glucose).

Question 5

Describe the conversions between glucose 1-phosphate, glucose 6-phosphate, and glucose.

Answer 5

1. Glucose 6-phosphate is used for glycolysis in most cells.
2. Liver cells convert glucose 6-phosphate into free glucose, which can leave the cell (glucose 6-phosphatase = enzyme responsible).
3. Phosphoglucomutase converts glucose 1-phosphate into glucose 6-phosphate.

Question 6

Describe phosphoglucomutase’s activity.

Answer 6

1. Enzyme has serine residue in active site which reversibly binds to phosphate in glucose depending on substrate/product concentrations.
2. Two steps reversible rxn: Glucose 1-phosphate glucose Glucose 6-phosphate

Question 7

How is the breakdown of glycogen regulated?

Answer 7

By activating glycogen phosphorylase through epinephrine and glucagon, which trigger intracellular signaling cascades.

Question 8

Describe the steps in activating glycogen phosphorylase.

Answer 8

1. Epinephrine binds to external cell membrane.
2. Internal cell membrane phosphorylates GDP –> GTP and dissociation of G-protein’s subunits beta and gamma
3. GTP-alpha activates adenylate cyclase to make cAMP
4. cAMP activates protein kinase A
5. Protein kinase A activates glycogen phosphorylase kinase
6. Glycogen phosphorylase kinase activates (via phosphorylation) glycogen phosphorylase.

Question 9

What is one benefit of a transduction cascade for glygogenolysis?

Answer 9

Each enzymatic step activates multiple molecules at once, so the results are amplification.