Final answer:
Cyclic AMP (cAMP) and Ca2+ are second messengers used in cells to propagate signals and regulate cellular activities. Cyclic AMP activates cAMP-dependent kinase (A-kinase) to phosphorylate target proteins, while Ca2+ activates protein kinases and influences cellular activities directly or through calcium-binding proteins.
Step-by-step explanation:
Second messengers are small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor. Cyclic AMP (cAMP) and Ca2+ are two important second messengers used in cells. Cyclic AMP is synthesized by adenylyl cyclase from ATP and activates an enzyme called cAMP-dependent kinase (A-kinase), which regulates vital metabolic pathways by phosphorylating target proteins. Ca2+ functions as a second messenger by activating protein kinases and influencing cellular activities directly or through calcium-binding proteins.