Question

the image above depicts the signal transduction pathway of epinephrine. during one step in the pathway, the enzyme glycogen phosphorylase is phosphorylated, which activates the enzyme.

if an inhibitor prevents glycogen phosphorylase from being activated during this pathway, which of the following will most likely occur?

choose 1 answer:

a) epinephrine will not bind to the epinephrine receptor.

b) glycogen synthase will be activated in place of glycogen phosphorylase.

c) blood glucose levels will not increase in response to epinephrine.

d) glycogen levels will decrease in response to epinephrine.

Explanation:

• Option A: Epinephrine binding to its receptor is an upstream event from glycogen phosphorylase activation. The inhibitor affects glycogen phosphorylase activation, not epinephrine - receptor binding. So A is incorrect.
• Option B: Glycogen synthase and glycogen phosphorylase have opposing roles (glycogen synthase synthesizes glycogen, glycogen phosphorylase breaks it down). Inhibiting glycogen phosphorylase activation does not mean glycogen synthase will be activated in its place as they are regulated by different mechanisms in this pathway. So B is incorrect.
• Option C: Glycogen phosphorylase is responsible for breaking down glycogen into glucose, which increases blood glucose levels. If an inhibitor prevents its activation, glycogen breakdown will be impaired, and blood glucose levels will not increase in response to epinephrine (which normally triggers this pathway to increase blood glucose). So C is correct.
• Option D: Since glycogen phosphorylase activation is inhibited, glycogen breakdown will not occur (or will be reduced). So glycogen levels should increase (or not decrease) rather than decrease in response to epinephrine. So D is incorrect.

Answer:

C. Blood glucose levels will not increase in response to epinephrine.