Final answer:
Cyclic AMP serves as an allosteric regulator for protein kinase A, facilitating various cellular responses by activating PKA, which phosphorylates target proteins. The signal is terminated by phosphodiesterase that converts cAMP into AMP.
b is correct
Step-by-step explanation:
Cyclic AMP is an allosteric regulator of protein kinase A (PKA). Once produced by the enzyme adenylyl cyclase from ATP, cAMP serves as a second messenger within cells. It binds to and activates cAMP-dependent kinase, also known as protein kinase A or PKA, by changing the kinase's structure to expose its active sites.
This activation allows PKA to phosphorylate target proteins, which can then lead to various cellular responses. Different cell types have different target proteins, which explains the variation in responses to cAMP. The signal induced by cAMP is terminated once the enzyme phosphodiesterase converts cAMP into AMP, thus halting its activity.