1. Plasma Membrane

2. Pre-Assessment
Which of the following statements concerning membrane proteins is incorrect?
They can act as a channel, allowing the transport of ions across the membrane.
They often require ATP to actively transport materials across the membrane against a concentration gradient.
They may be receptor proteins that bind specific molecules from the surrounding solution, which triggers endocytosis (i.e., receptor-mediated endocytosis).
They are usually not particular about what types of chemicals they will allow to cross the membrane.

3. 2. Which molecule works to keep the membrane at optimal fluidity. 3
2. Which molecule works to keep the membrane at optimal fluidity? 3. Which molecule is both hydrophobic and hydrophilic and aggregates as a bilayer to form the "fabric" of the membrane? 4. Which molecule may function in facilitated diffusion? 5. Which molecule might serve as a binding site for a hormone, thereby eliciting a response in the cell?

4. Phospholipid Bilayer
Composed of fatty acid tails connected to glycerol heads
non-polar (hydrophobic) fatty acid interior impedes passage of water-soluble substances (it is liquid like a soap bubble)
Polar heads (hydrophilic) are water soluble

5. Components of a Plasma Membrane
Phospholipids
Proteins
Integral proteins – completely penetrate the lipid bilayer; they control the entry and removal of specific molecules
Peripheral proteins – bound to the exterior surface of the membrane; they have various functions

6. Components of a Plasma Membrane
Cholesterol
Inside near the fatty acid tails; helps to regulate membrane fluidity and is important for membrane stability

7. Fluid Mosaic Model

8. The 6 Membrane Protein Functions
Hormone binding sites – these proteins have specific shapes exposed to the exterior that fit the shape of specific hormones
Enzymes – catalyze chemical reactions; may be on interior or exterior of the cell membrane; often grouped together for a chain reaction (called metabolic pathway)
Cell adhesion – proteins hook together to provide temporary or permanent connections; these connections referred to as junctions

9. 4. Cell-to-cell communication – many include carbohydrates attached to protein molecules on outside of cell; they provide an ID tag letting other cells know what type of cell they are 5. Channels for passive transport – integral proteins that have a channel in them to allow substances to move through; passive means substances move through from high to low concentration 6. Pumps for active transport – integral proteins that shuttle a substance from one side to the other by changing their shape; this process requires energy in the form of ATP

10. Diffusion and Osmosis
Diffusion: passive movement of particles from high to low concentrations
Osmosis: passive movement of WATER molecules from low solute concentration to high solute concentration

11. Passive Transport
Membranes are semi permeable so only certain molecules can pass through
Passive Transport = NO ENERGY
Simple Diffusion: movement of molecules through the phospholipid bilayer
Hydrophobic molecules use this method

12. Types of Diffusion
Facilitated Diffusion: movement of molecules with the help of a protein channel found in the membrane
Hydrophilic molecules use the channel proteins

13. Protein Pumps and ATP
Active Transport: movement of substances through the membrane using energy (ATP)
Substances are moved against their concentration gradient
LOW to HIGH concentrations
Possible because of membrane protein pumps
Pumps are selective as well

14. Vesicles Once proteins are synthesized by ribosome:
Transported to the rough ER to be modified
Vesicles with the protein bud off of the rough ER and are transported to the Golgi Apparatus for more modification
Then, the vesicle transports the protein to the membrane by fusing with the membrane and expelling the contents outside the cell
The membrane reforms

15. Endocytosis and Exocytosis
The membrane is fluid to allow it to change shape
Exocytosis: the vesicles fuses with the membrane and expells the contents OUT of the cell
Endocytosis: the pulling of the plasma membrane INWARDS so a vesicle is pinched off it and can carry the contents INTO the cell