Biochemistry Question

Question

b.) Describe the process of glycogenolysis step by step. [10]

Answer 1

1. Glycogen phosphorylase catalyzes the release of glucose-1-phosphate from the terminal residue of a nonreducing end of a glycogen branch, by means of phosphorolysis. A molecule of inorganic phosphate attacks the C₁ side of an α(1→ 4) glycosidic bond leaving a hydroxyl group on C₄ that remains in the glycogen polymer.Glucose-1-phosphate is converted by phosphoglucomutase to glucose-6-phosphate. glucose-6-phospate may enter glycolytic pathway or if glucose-6-phosphatase is present, free glucose can be formed,Glucose residues are phosphorolysed from branches of glycogen until four residues before a glucose that is branched with a α-[1→6] linkage. Glycogen de-branching enzyme then transfers three of the remaining four glucose units to the end of another glycogen branch.This exposes the α-[1→6] branching point, which is hydrolyzed by α[1→6] glucosidase, removing the final glucose residue of the branch as a molecule of glucose and eliminating the branch.The glucose is subsequently phosphorylated to glucose-6-phosphate by hexokinase.