1. AP Biology Chapter 7 The Cell Membrane

2. AP Biology Overview  Plasma membrane separates living cell from nonliving surroundings  thin barrier = 8nm thick  Controls traffic into & out of the cell  selectively permeable  allowing some substances to cross more easily than others  Made of phospholipids, proteins & other macromolecules

3. AP Biology Phospholipids  Fatty acid tails are hydrophobic  Phosphate group form a hydrophilic head  interaction with H 2 O is complex  & very important!

4. AP Biology Phospholipids in water  At surface of a cell phospholipids are arranged as a bilayer  hydrophilic heads on the outside in contact with aqueous solution & hydrophobic tails form core  phospholipid bilayer forms a barrier between cell & external environment

5. AP Biology Fluid Mosaic Model  In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer

6. AP Biology A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

7. AP Biology Membrane Proteins  Proteins determine most of membrane’s specific functions  Plasma membrane & organelle membranes each have unique collections of proteins  Membrane proteins:  peripheral proteins = loosely bound to surface of membrane  integral proteins = penetrate into lipid bilayer, often completely spanning the membrane (a transmembrane protein)

8. AP Biology Why are proteins the perfect molecule to function embedded in the cell membrane?

9. AP Biology 2005- 2006 Why proteins?  Proteins are mixed molecules  hydrophobic amino acids  stick in the lipid membrane  anchors the protein in membrane  hydrophilic amino acids  stick out in the watery fluid in & around cell  specialized “receptor” for specific molecules

10. AP Biology

11. 2004-200 Integral Proteins  Within membrane  hydrophobic regions with nonpolar amino acids  often coiled into alpha helices  Outer surfaces of membrane  hydrophilic regions with polar amino acids

12. AP Biology 2004-200 Inside & outside surfaces are different  2 layers may differ in lipid composition  proteins in membrane have a direction  outer surface also has carbohydrates

13. AP Biology Membranes provide a variety of cell functions

14. AP Biology Fluid membranes  Permeability  membrane must be fluid, about as fluid as salad oil  Changing temperatures  cells alter lipid composition of membranes  cold-adapted organisms  winter wheat increases % unsaturated phospholipids in autumn  prevent membranes from solidifying during winter

15. AP Biology Unsaturated fats  more fluid membranes  kinks in unsaturated fatty acid tails prevent tight packing

16. AP Biology Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish neighboring cells from another  important in organ & tissue development  basis for rejection of foreign cells by immune system

17. AP Biology 2004-20 A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

18. AP Biology Any Questions??