Glycogen Metabolism Flashcards
The breakdown of glycogen to release sugar
glycogenolysis
Which hormone activates glycogenolysis
glucagon
What is the role of glycogen phosphrylase during glycogenolysis?
This enzyme cleaves a single a1->4a glycosidic bond (at the nonreducing end) of glycogen to form glucose 1-phosphate.
What is the role of the debranching enzyme?
The debranching enzyme cleaves the a1->6 glycosidic bond. It transfers 3 linear carbons onto the end of the chain and cleaves the branching glucose to generate a free glucose.
Describe the steps of glycogenesis.
I. UDP molecule is bounded to G1P by UDP-glucose pyrophosphorylase to form UDP-glucose.
II. UDP-glucose is added to the nonreducing end of a glycogen chain by glycogen synthase.
What would happen if glycogenin is not present during glycogenesis?
Glycogenin is a primer require for the synthesis of glycogen. Even in the presence of UDP-glucose and glycogen synthase, without this primer, UDP-glucose cannot be added onto the growing glycogen chain.
If a patient has a glycogen storage disease that result in the formation of a1-4 glycosidic bonds only. What enzyme is likely affected by this disease.
branching enzyme
How is glycogen phosphorylase regulated?
During high levels of blood glucose, insulin activates PP1 which activates phosphorylase a phosphatase. This enzymes catalyzes the dephosphorylation of phosphorylase a into phosphorylase b to decrease glycogenolysis.
During low levels of blood glucose, glucagon activate PKA which actives phosphorylase b kinase. This enzyme catalyzes the phosphorylation of phosphorylase b into phosphorylase a.
How is glycogen synthase regulated?
1, Insulin, glucose and G6P activate PP1 which dephosphorylate glycogen synthase b into glycogen synthase a. This activates glycogenesis.
2. Glucagon and epinephrine activate PKA which phosphorylase glycogen synthase a into glycogen synthase b. This inhibits glycogenesis.
