The figure below shows a segment of glycogen. Each residue is numbered. Give the

Question

The figure below shows a segment of glycogen. Each residue is numbered. Give the residue numbers of the first two residues released from the chain as glucose-1-phosphate molecules. How many residue/s will be released from the chain as glucose? Give the residue number/s. List all. Can the branching enzyme create a new branch on the glycogen segment above? If yes, please give the location of the new branch, if not, then explain why not. Residues 1, 2, and 3 may be cleaved as a trisaccharide by debranching enzyme. True/False. Explain in one short sentence. Which end may glycogenin be linked to? Please circle in the above structure. Glycogenin primes the synthesis by reacting with ghuose-6-phosphate. True/False. Explain in one short sentence. During degradation, the G6P formed may be converted to glucose in the muscle and the liver. True/False. Explain in one short sentence. The energy cost of extending the glycogen chain by one glucose residue is the cleavage of one phosphoanhydride bond. True/False. Explain in one short sentence.

Explanation / Answer

During glycogenolysis, glycogen phosphorylase acts on glycogen molecule. This enzyme removes glucose molecules as glucose1-phosphate.

A) The first molecules removed as glucose 1-phosphate will be residues 1, 2 and 7.

B) Glycogen phosphorylase cannot remove glucose residues which are 4 residues away from the branch point. Now, the debranching enzyme starts its action. It removes residues 3, 4 and 5 as a trisaccharide; and attaches these to the main chain. Now it removes, residue no. 6 as glucose.

Only one residue will be removed as glucose in the above case.

C) No, glycogen branching enzyme will not make another branch. This is because the enzyme creates a branch after 10-14 residues of glucose. In the above case, this many long residue chain is not there.

D) The statement is false. The correct statement is "Residues 3, 4 and 5 will be removed as trisaccharide by the debranching enzyme".

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