Receptor Protein - Protein that binds to a specific single molecule, enabling the cell to respond to the signal molecule. i. e. - The muscles of a person exercising can not contract without receptor proteins and signal molecules that tell the muscles when to contract and when to relax. Second Messenger - Signal molecule produced in response to the binding of a chemical signal. Acts as a signal molecule in the cytoplasm.

Signal Molecule - Carries information throughout the body and to other cells. Ion Channel - A large protein in the cell membrane that transports a specific ion. Enzyme Action - Speeds up chemical reactions in the cell Beta Blocker - A drug that interferes with the binding of signal molecules to receptor proteins and heart muscles. Changes in permeability - Occur when a receptor protein is coupled with an ion channel. Functions of receptor proteins The signal molecule binds to the receptor protein that's specialized to fit the molecule.

Binding of a signal molecule to the matching receptor protein causes a change in the activity of the receiving cell in three ways: 1. Changes in permeability of receiving cell 2. Triggering the formation of second messengers inside the cell 3. Activating the enzymes inside the cell 1. Changes in Permeability An Ion Channel may be coupled with the receptor protein, is in Figure 4-8 on Pg.

84. The binding of the second messenger and the receptor protein causes the Ion Channel to open. This allows specific ions to cross the cell membrane. 2. Second Messengers Receptor protein can cause a second messenger to form inside of the cell. Some second messengers activate enzymes, triggering a series of biochemical reactions in the cell.

They can also change the permeability of cells by opening ion channels in the cell membrane. 3. Enzyme action The receptor protein may act as an enzyme. Receptor proteins can speed up chemical reactions inside of the cell when it is combined with a signal molecule. It may also activate other enzymes located in the cell or cell membrane.