regulatory molecules Some regulatory substances enter the cell and bind to receptors Agonists exert their effects on cells via signal- transduction pathway, whereby the binding of an agonist to its plasma membrane receptor elicits an intracellular response by altering the activities of particular cellular proteins.• Some regulatory substances enter the cell and bind to receptors ➢ regulatory molecules • Agonists exert their effects on cells via signal￾transduction pathway , whereby the binding of an agonist to its plasma membrane receptor elicits an intracellular response by altering the activities of particular cellular proteins