18. True or false? The binding of epinephrine to its membrane bound receptor eve

Question

18. True or false? The binding of epinephrine to its membrane bound receptor eventualy leads to inactivation of that receptor, a phenomenon known as down regulation 19. True or false? If a person lacks the glycogen branching enzyme (thereby leaving their glycogen polymers unbranched and much less soluble), then that person suffers from what is broadly categorized as a glycogen storage disease. 20. True or false? The dual purpose of the pentose phosphate shunt is to provide six-carbon sugars and to generate NADPH Short Answer 21. Uridine diphosphate glucose (UDP-glucose) is one of the intermediates in the synthesis of glycogen from glucose-6-P. Why is UDP-glucose considered to be activated glucose? 22. Complete de novo synthesis of the glycogen molecule requires a dimeric protein called glycogenin. What two roles does glycogenin play in glycogen synthesis?

Explanation / Answer

UDP-glucose is the activated form of glucose used in Glycogen synthesis as a glucose donor. The reaction of glucose 1-phosphate and uridine triphosphate (UTP), catalysed by UDP-glucose pyrophosphorylase, forms UDP-glucose by the removal of two phorphoryl groups from the UTP [1] . Glucose 1-phosphate + UTP + H20 --------> UDP-glucose + 2Pi

Glycogen synthase catalyses the formation of glycogen by adding the activated glucosyl unit from the UDP-glucose to the hydroxyl group on the carbon-4 atom of the glycogen molecule.

Glycogen synthesis reaction: Glycogenn + UDP-glucose ----> glycogenn+1 + UDP

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