Question

In glycogenesis, how is the direction of the pathway pushed in the forward direction to glycogen synthesis?

Group of answer choices

a. A UTP molecule is added to glucose to make UDP-glucose

b. The alpha(1,4) linkage step is tied to ATP hydrolysis

c. The mutase step rearranges the location of the phosphate group on glucose

d. The activation step is made irreversible via Ppi hydrolysis

Answer 1

In glycogenesis, the pathway towards glycogen synthesis is driven forward by the irreversible hydrolysis of PPi, which occurs during the formation of UDP-glucose from glucose-1-phosphate.

Step-by-step explanation:

In glycogenesis, the pathway is pushed forward toward glycogen synthesis through the activation of glucose. This activation is achieved by the formation of UDP-glucose. The pathway entails the initial phosphorylation of glucose to form glucose-6-phosphate, which is then converted to glucose-1-phosphate by the action of phosphoglucomutase. This is followed by the coupling of glucose-1-phosphate to uridine triphosphate (UTP) by the enzyme glucose-1-phosphate uridyl transferase, leading to the creation of UDP-glucose and the release of pyrophosphate (PPi).

The conversion is made irreversible through the hydrolysis of PPi, a reaction catalyzed by inorganic pyrophosphatase. This reaction is highly exergonic, which drives the overall direction of the pathway forward, thus making the conversion of glucose to glycogen energetically favorable. The hydrolysis of PPi ensures that the reaction does not easily reverse, cementing the pathway's direction towards glycogen synthesis and preventing the reconversion back to glucose or glucose-6-phosphate.

The correct answer to the student's question is d. The activation step is made irreversible via PPi hydrolysis.