Secondary messenger: Some hormones are proteineceous in nature are known as primary messenger, they are unable to pass through the plasma membrane so they bind to the specific receptor site on the cell surface of the target cell. This binding is a signal that increases the concentration of another metabolic in the cytoplasm called secondary messenger. The secondary messenger activates the related enzymes. Till now two secondary messengers are known: cyclic adhesive monophosphate (CAMP) and Ca+2. CAMP is restricted to animal cells and bacteria whereas Ca+2 act as secondary messenger in all living organisms.
In the cytoplasm, CAMP acts as secondary messenger which binds to and activates enzyme protein kinase. The activated protein kinase enzyme which in turn converts the inactive form of glycogen phosphorylase into its active form. This increase the rate of glycogen breakdown into glucose. In eucaryotes, calcium is involved in the regulation of processes such as cell growth, cell division and cell motility. The enzymes are regulated by a calcium binding protein of small, lower molecular weight, that modulates the effect of cytoplasmic calcium. This protein is known as calmodulin.