2. Cell Membranes Separates the Inside of the cell from the outside of the cell

3. Permeability Permeable Membranea membrane which allows particles to travel freely through the membrane (they can go back and forth) Impermeable Membranea membrane which DOES NOT allow particles to travel freely through the membrane (they are stuck on one side or the other)

4. Selective Permeability Characteristic of cell membranes Ability to regulate the passage of molecules Allows some molecules to pass through the membrane, but not others

5. The Cell Membrane Known as the Lipid Bilayer Composed of fat (lipid) molecules Lipid molecules drift randomly in the plane of the membrane (they arent attached)

6. The Lipid Bilayer Exterior Layer Part of the fat molecules that LIKE water are located on the outside (the round heads) They are called Polar Molecules

7. The Lipid Bilayer Internal Layer Part of the fat molecules that DONT LIKE water are located on the inside They are called Non-Polar Molecules Prevents Water-Soluble (things that dissolve in water) molecules from passing through the membrane Fat-Soluble molecules pass through easily!

8. One Exception! Water molecules CAN pass through the membrane Very SMALL molecules VERY SLIGHT electrical charge

9. Proteins Large molecules made up of amino acids that are linked together to form a long, folded chain These are the big masses that stick out of the membrane Act as Receptors

10. Receptors Bind specifically to molecules, such as hormones, that act as chemical messengers Receptors receive a message Hormones attach to receptors Triggers the cell to respond to some body condition

11. Protein Function Cont. Allow specific molecules to move in and out of the cell Allow the membrane to be Selectively Permeable (It can choose what it wants to go in and out)

12. Protein Function #2 Form Specific Protein Channels –Gives Large Molecules a way to pass through the lipid bilayer –Ex. Glucose and Sugar –Ion Channels Ions molecules with an electric charge Need a channel b/c fat cells repel their charge

13. Parts of the Lipid Bilayer You dont have to sketch this, but make sure that you are familiar with it!