In Mammals, the Hormone Epinephrine Activates an Intracellular Signalling Pathway

Multiple Choice

In mammals, the hormone epinephrine activates an intracellular signalling pathway that leads to the breakdown of glycogen in the liver. The binding of epinephrine to a G-protein linked receptor on the surface of liver cells activates a succession of relay molecules including the adenyl cyclase, cAMP and protein kinase A, The final protein to be activated is the enzyme glycogen phosphorylase, which catalyses the breakdown of glycogen to glucose-1-phosphate. In this signalling pathway, the second messenger is

A) the G-protein.
B) active protein kinase A.
C) adenyl cyclase.
D) cAMP.
E) glycogen phosphorylase.