Answer to Question #223778 in Cell Biology for Payal Kaushik

Question #223778

Discuss how the body breaks down glycogen.

Expert's answer

Glycogen breakdown consists of three major steps and uses four different enzymes. The first step of glycogen breakdown is phosphorolysis, which is catalyzed by an enzyme called glycogen phosphorylase. This enzyme uses an orthophosphate to cleave an alpha 1,4 - glycosidic bond between a terminal glucose with a free hydroxyl on the 4th carbon and thus the adjacent glucose. The products of this reaction are a glucose 1-phosphate and a glycogen that contains one less glucose. Glycogen phosphorylase can only cleave alpha 1,4 glycosidic bonds; it cannot cleave the alpha 1,6 glycosidic bonds that structure the branching points. In fact, glycogen phosphorylase stops cleaving the glycogen four glucose residues faraway from a branching point. In the second step of glycogen breakdown, two enzymes - transferase and alpha 1,6 glucosidase - help modify the glycogen in order that glycogen phosphorylase can continue the degradation process. Transferase removes a gaggle of three glucose molecules and transfers it onto the other branch of glycogen. Alpha 1,6 glucosidase removes the remaining glucose molecule by cleaving the alpa 1,6 glycosidic bond. In the final step, an enzyme called phosphoglucomutase converts the glucose 1-phosphate into glucose 6-phosphate.

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