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