(Science: molecular biology) 3'5' cyclic ester of amp. The first second messenger hormone signalling system to be characterised. Generated from atp by the action of adenyl cyclase that is coupled to hormone receptors by G-proteins (GTP-binding proteins). Camp activates a specific (camp dependent) protein kinase and is inactivated by phosphodiesterase action giving 5'AMP. Also functions as an extracellular morphogen for some slime moulds.