Glycogen breakdown and formation

Question 1

What are the steps of glycogenolysis?

- breakdown of glycogen

Answer 1

1. Glycogen phosphorylase
   - Glycogen chain
   - You add glycogen phosphorylase and phosphorylase catalyses the covalent addition of inorganic phosphate to a molecule
   - You then get a glucose molecule that breaks off from this glycogen chain (glucose-1-phosphate) and a shortened glycogen chain
2. Debranching enzyme
   - Has transferase activity
   - Transfers a block of 3 glucose residues to a nearby nonreducing end
   - Hydrolyses the a1-6 linkage to release free glucose
3. Phosphoglucomutase
   - Must involve a transfer of a phosphoryl group within the same molecule
   - Transfers a phosphoryl group on glucose-1-phosphate from C-1 to C-6 to form glucose-6-phosphate

Question 2

What are the steps of glycogenesis?

- formation of glycogen from glucose

Answer 2

1. UDP-Glucose Pyrophosphorylase
   - Glucose-1-Phosphate + UTP -> the UTP loses two of its phosphate groups
   - The glucose-1-phosphate becomes attached to the remaining phosphate group on the former UTP and UDP-glucose is produced

• The pyrophosphate is unstable and can break down into two phosphates

2. Glycogen synthase (synthesising glycogen)
   - The glycogen synthase takes the UDP-glucose and adds it to the glycogen particle
   - Binds a long chain of glucose monomers that are a1-4 linked (puts glucose on the nonreducing end)
   - UDP is released
3. Glycogen branching enzyme
   - Catalyses the transfer of a block of 6 or 7 glucose residues from the nonreducing end of a glycogen branch having at least 11 residues to the C-6 hydroxyl group in a more interior position within the same or a different glycogen chain