Which statement is TRUE of glycogen synthesis and breakdown?
A) Phosphorylation activates the enzyme responsible for breakdown, and inactivates the synthetic enzyme.
B) Synthesis is catalyzed by the same enzyme that catalyzes breakdown.
C) The glycogen molecule "grows" at its reducing end.
D) The immediate product of glycogen breakdown is free glucose.
E) Under normal circumstances, glycogen synthesis and glycogen breakdown occur simultaneously and at high rates.

Question

Quizplus · Accepted Answer

Phosphorylation activates glycogen phosphorylase, the enzyme responsible for glycogen breakdown, and inactivates glycogen synthase, the enzyme responsible for glycogen synthesis. Choice B is false as synthesis and breakdown are catalyzed by separate enzymes. Choice C is true, as glycogen synthesis occurs at the reducing end of the growing glycogen molecule. Choice D is false as the immediate product of glycogen breakdown is glucose-1-phosphate, which must be converted to free glucose before it can be used as fuel by cells. Choice E is false as glycogen synthesis and breakdown are typically regulated to occur at different times to prevent futile cycling.

Which Statement Is TRUE of Glycogen Synthesis and Breakdown