<prompt> Second messenger isare:Ca2DNAHistonecDNA  <response>: Ans: a. Ca2 Ref Harper 30th501, 91-92, 179, 343; Lippincott 6th94-951Nucleotides, such as cyclic adenosine mono-phosphate cAMP and cyclic guanosine monophosphate cGMP, serve as second messengers in signal transduction pathways.Two of the most widely recognized second messenger systems are the calciumlphosphatidy linositol system, and the adenylyl cyclase system, which is paicularly impoant in regulating the pathways of intermediary metabolism. 