AP BIOLOGY

Detailed explanation-1: -In the center, binding of ligands to a GPCR (receptor) activates phospholipase C (PLC; the effector), to generate two second messengers, DAG and IP3, which activate protein kinase C (PKC; the target) and release calcium from intracellular stores, respectively.

Detailed explanation-2: -Calcium ion (Ca(2+)) plays an important role in stimulus-response reactions of cells as a second messenger. This is done by keeping cytoplasmic Ca(2+) concentration low at rest and by mobilizing Ca(2+) in response to stimulus, which in turn activates the cellular reaction.

Detailed explanation-3: -Cyclic AMP (cAMP) and calcium (Ca2+) are arguably the prototypical second messengers that control cellular homeostasis. Whereas, for instance, nitric oxide and cyclic GMP may serve essential functions in a number of physiological situations, cAMP and Ca2+ are the only truly ubiquitous second messengers.