what hormone cannot diffuse through the plasma membrane
Nonsteroid hormones, in general, cannot diffuse across the plasma membrane and therefore must interact with membrane receptors . Receptors of this type are usually transmembrane proteins that contain a hormone-binding domain outside of the cell and another domain inside of the cell that changes its shape when the hormone is bound. It subsequently causes other changes in the cell, usually by activating enzymes through a chemical intermediary. Since the hormone is not causing the changes directly, the intermediary is often referred to as a second messenger (the hormone being the âfirst messengerâ).