1. Receptor Proteins Receiving and responding to messages

3. Receptor Proteins • Proteins in the cell membrane which receive incoming “messages” • Cells communicate with each other by sending specific signal molecules to each other. • These molecules bind to specific receptor proteins. Membrane Signal molecules Receptor Protein

4. Signal molecules could be: • Hormones • Ions • Neurotransmitters • Nutrients • Drugs

5. When the signal molecule binds to the receptor protein, what could happen? 1. Change the permeability of the membrane: Allowing certain substances into the cell. For example, the hormone insulin binds to a receptor protein. This causes a protein channel to open and allow glucose into the cell.

6. 2. A receptor protein may activate a second messenger in the cell: The signal molecule binding to the receptor protein sets off a chain reaction, which could be a series of several reactions within the cell. http://www.youtube.com/watch?v=HnnMOx9_eBY

7. 3. Enzyme Action: The receptor protein might also be an enzyme that changes the signal molecule or triggers a reaction inside the cell. http://www.dnalc.org/resources/3d/cellsignals.html

8. How do you think receptor proteins are important in the digestive system? Where would you expect to find receptor proteins in the digestive system?