Peptides intracellular messengers used

The structural properties of a messenger determine, to some extent, the type of receptor it binds. Most receptors fall into two broad categories intracellular receptors or plasma membrane receptors (Fig. 11.7) Messengers using intracellular receptors must be hydrophobic molecules able to diffuse through the plasma membrane into cells. In contrast, polar molecules such as peptide hormones, cytokines, and catecholamines cannot rapidly cross the plasma membrane and must bind to a plasma membrane receptor. 

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