2. AP Biology 2007-2008 Ch. 5.1 Plasma Membrane Structure and Function

3. AP Biology Membrane Design 2 fluid-mosaic model a. Fluid = pliable/easily moved - due to lipid component -phospholipids can move laterally b. Mosaic = made of a combination of molecules (lipids, proteins, and carbs) Cell Membrane Animation

4. AP Biology Phospholipids Fatty acid Phosphate  Phosphate head  hydrophilic  Fatty acid tails  hydrophobic  Arranged as a bilayer “repelled by water” “attracted to water”

5. AP Biology Arranged as a Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads  Serves as a cellular barrier / border H2OH2O sugar lipids salt waste impermeable to polar molecules

6. AP Biology Cell membrane defines cell  Cell membrane separates living cell from aqueous environment  thin barrier = 8nm thick  Controls traffic in & out of the cell  allows some substances to cross more easily than others  hydrophobic (nonpolar) vs. hydrophilic (polar)

7. AP Biology Permeability to polar molecules?  Membrane becomes semi-permeable via protein channels  specific channels allow specific material across cell membrane inside cell outside cell sugaraa H2OH2O salt NH 3

8. AP Biology Membrane Proteins  Proteins determine membrane’s specific functions  cell membrane & organelle membranes each have unique collections of proteins  Classes of membrane proteins:  peripheral proteins  loosely bound to surface of membrane  ex: cell surface identity marker (antigens)  integral proteins  penetrate lipid bilayer, usually across whole membrane  transmembrane protein  ex: transport proteins  channels, permeases (pumps)

9. AP Biology 8 Example: Aquaporins let water in and out of the cell

10. AP Biology 9 Proteins with carbohydrate chains attached; carb chains act as ID markers AKA Glycoproteins Receive chemical signals (neurotrasmitters/hormones) to deliver messages from cell to cell

11. AP Biology 10

12. Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  Allows cells to stick to eachother (adhesion)  important in organ & tissue development  Glycoproteins and glycolipids  basis for rejection of foreign cells by immune system

13. AP Biology Cholesterol  Modifies fluidity  High temp – stiffens membrane  Low temp – prevents membrane from freezing

14. AP Biology Extracellular Matrix  Only in Animal cells  Area between cells  Contain various protein fibers and complex carbohydrates  Function: assists in communication between cells

15. AP Biology Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids

16. AP Biology Any Questions??

17. AP Biology Plasma Membrane Structures 16 1. Phospholipids a. polar heads are hydrophilic “water loving” b. tails (fatty acids) are hydrophobic “water fearing” and directed inward 2. Extracellular Matrix (ECM) Only animal cells Contain various protein fibers and complex carbohydrates Function: assists in communication between cells 3. Carbohydrate Chains Glycoproteins and glycolipids Only occur on outside surface of cell membrane Function: Adhesion between cells Reception of signaling molecules Cell to cell recognition

18. AP Biology Plasma Membrane Structures 17 4. Cholesterol  Lipid  Modifies fluidity  High temp – stiffens membrane  Low temp – prevents membrane from freezing 5. Proteins -serves many different functions  Integral  Peripheral