2. The Cell Membrane

3. Phospholipids Phosphate head hydrophilic Fatty acid tails hydrophobic Arranged as a bilayer “repelled by water” “attracted to water” Aaaah, one of those structure–function examples

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

5. Cell membrane defines the cell Cell membrane separates the living cell from the aqueous environment Thin barrier = 8 nm thick Controls movement in & out of the cell Allows some substances to cross more easily than others Hydrophobic (nonpolar) vs hydrophilic (polar)

6. Permeability to polar molecules Membrane becomes semipermeable via protein channels Specific channels allow specific material across the membrane inside cell outside cell sugaraa H2OH2O salt NH 3

7. More to membrane than phospholipid bilayer Transmembrane proteins embedded in phospholipid bilayer Create semi-permeable channels lipid bilayer membrane protein channels in lipid bilyer membrane

8. Why are proteins the perfect molecule to build structures in the cell membrane?

9. It’s all in the amino acids What do these amino acids have in common? nonpolar & hydrophobic

10. It’s all in the amino acids What do these amino acids have in common? polar & hydrophilic I like the polar ones the best!

11. Amino acids anchor proteins Within membrane Nonpolar amino acids Hydrophobic Anchors protein into membrane On surface of membrane Polar amino acids Hydrophilic Extend into extracellular fluid & into cytosol Polar areas of protein Nonpolar areas of protein

12. Examples NH 2 H+H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic)  -helices in the cell membrane H+H+ Porin monomer  -pleated sheets Bacterial outer membrane proton pump channel in photosynthetic bacteria aquaporin = water channel in bacteria function through conformational change = protein changes shape H2OH2O H2OH2O H+H+ H+H+

13. Many functions of membrane proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion “Antigen” “Channel”

15. 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 bilayer, usually across the whole membrane Transmembrane proteins  Ex. Transport proteins

16. What else is in the membrane? Cholesterol Increases flexibility of cell membrane Temperature sensitive c

17. What else is in the membrane? Glycoproteins Have carbohydrate chains Important in cell-to-cell recognition Basis for rejection of foreign cells by immune systems c c

18. What else is in the membrane? Glycolipids Carbohydrate chains Important in cell-to-cell recognition Help determine blood type Involved with immune system c c

19. There’s so much there … It’s like a mosaic … But, it’s still fluid in its movement It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model!

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

21. Any Questions??