There is an immediate energetic advantage to muscle in using its own glycogen st

Question

There is an immediate energetic advantage to muscle in using its own glycogen stores in glycolysis rather than glucose from the bloodstream. Which statement accurately explains why this is so?

a. Glucose transport into muscle cells is an active transport process.

b. Glycogen is broken down by phosphorolysis and this reduces the number of ATP molecules that must be invested in the hexoses stage of glycolysis.

c. Glycogen is broken down to glucose-1-phosphate, which is a high-energy intermediate.

d. UDP-glucose is a high-energy intermediate which includes a phosphoanhydride bond equivalent to that in ATP.

Explanation / Answer

Glycogen is broken down by phosphorolysis and this reduces the number of ATP molecules that must be invested in the hexoses stage of glycolysis.

Explanation:
It is broken down to glucose-1-phosphate which can be converted to G6P by phosphoglucomutase. In muscle, this G6P is used directly for glycolysis. In liver, when blood glucose is low, G6P is hydrolyzed to glucose by glucose-6-phosphatase, and the resulting glucose is exported into the bloodstream for use in other tissues. Glucose-6-phosphatase is absent in muscle.

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