Practice question

Second messengers are small, diffusible intracellular molecules generated in response to receptor activation. Classic examples include cyclic AMP, cyclic GMP, inositol 1,4,5-trisphosphate, diacylglycerol and Ca2+. Hormones such as insulin act as primary messengers and are not themselves second messengers. The rapid rise and fall of second-messenger concentrations allow precise temporal control of downstream signaling pathways.