Peptide hormones,”Peptide hormones never enter a cell so they bind to a receptor protein in plasma membrane. Epinephrine binds to receptor protein; relay system leads to conversion of ATP to cyclic AMP. Cyclic AMP (cAMP) is made from ATP; it has one phosphate group attached to adenosine at two locationsPeptide hormones are the first messenger; cAMP and calcium are often the second messengercAMP sets an enzyme cascade in motion.. Activated enzymes can be used repeatedly
resulting in a thousand-fold response.”