[Campbell Biology P.276] In the epinephrine signaling pathway Figure 11.16 , if a drug speci... | Practice Question

In the epinephrine signaling pathway Figure 11.16 , if a drug specifically inhibited the ability of active protein kinase A to phosphorylate and activate phosphorylase kinase, what would be the most immediate and significant consequence?

  • A: Cyclic AMP (cAMP) production would cease entirely.
  • B: Glycogen phosphorylase would remain in its inactive form, preventing glucose 1-phosphate release.
  • C: Epinephrine would no longer bind to its G protein-coupled receptor.
  • D: Inactive G protein would be unable to become active.

Explanation

Protein kinase A acts as a relay molecule that activates phosphorylase kinase. If this step is inhibited, the cascade stops here. Consequently, phosphorylase kinase would not be activated, and thus glycogen phosphorylase, which is activated by phosphorylase kinase, would remain inactive. This would prevent the breakdown of glycogen into glucose 1-phosphate, halting the cellular response to epinephrine.