University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

165

Pages:

5
Author:

Sheha A.

Glycogenolysis It is the breakdown of glycogen. * Tissue Site: Liver and muscle * Intracellular Site: Cytosol * Starting material: Glycogen * And product: (i) Glucose in liver (ii) Glucose 6-phosphate in muscle (muscle does not contain glucose 6-phosphatase enzyme) Reaction Pathway * Glycogen is broken down by the combined action of 3 enzymes: * a) glycogen phosphorylase * b) glycogen transferase * c) debranching enzyme a) Glycogen phosphorylase: * It acts on glycogen and breaks the terminal α(1→4) glycosidic bonds of glycogen and releases the terminal molecule as glucose 1-phosphate. * Action of glycogen phosphorylase continues till only a glucose residue remains on either side of the branch point. b) Glycogen transferase: * It transfers glucose residues from one chain to another chain and thus exposing a (1→4) glycosidic bond. c) Glycogen debranching enzyme: * It splits a (1→6) glycosidic bond of the branch point and releases a glucose residue for the removal of branch and action of glycogen phosphorylase continues. * Thus the action of three enzymes leads to the complete breakdown of glycogen to give glucose 1-phosphate molecules and few free glucose molecules. Fate of glucose 1-phosphate: a) In liver: Glucose 1-phosphate is converted to glucose by glucose 6-phosphatase. b) In muscle: Muscle lacks glucose 6-phosphatase enzyme, so the end product of muscle glycogenolysis is glucose 6-phosphate.