Signaling by interaction of membrane- bond molecules. Subtype is autocrine, where a transmitter released by a cell affects that cell.
Endocrine systems can use either water soluble or hydrophobic signals.
No- turns out that there is an inhibitor protein which falls off in binding hormone, exposing a DNA binding site. This is sufficient. Cell Surface Receptors 1. Hydrolysis of GTP 2. CAMP- 1 example 2.