Which of the following statements is true?
A) Glycogen phosphorylase in liver cells is always active.
B) cAMP is referred to as a "first messenger."
C) Epinephrine directly activates adenylyl cyclase.
D) cAMP is referred to as a "second messenger."
E) Adenylyl cyclase is a protein kinase.

Question

Quizplus · Accepted Answer

cAMP is a second messenger that is produced when a signaling molecule (the first messenger) binds to a receptor on the cell surface. The second messenger then helps to relay the signal inside the cell, often by activating protein kinases or other enzymes. Glycogen phosphorylase in liver cells is not always active, and its activity is regulated by several factors including hormones and cellular energy levels. Epinephrine indirectly activates adenylyl cyclase by binding to a G protein-coupled receptor, which then activates adenylyl cyclase to produce cAMP. Adenylyl cyclase is not a protein kinase, but rather an enzyme that catalyzes the conversion of ATP to cAMP.

Which of the Following Statements Is True