1. Membrane Structure & Function
Chapter 7

2. Membrane Structure
fluid mosaic model – a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

3. Phospholipids amphipathic – hydrophobic & hydrophilic regions
arrange themselves so that the hydrophobic tails face away from water
bilayer is held together by weak hydrophobic interactions

4. Membrane Fluidity
most of the lipids & some of the proteins drift laterally
lateral movement of phospholipids is rapid
lateral movement of proteins is slow
flip-flopping of phospholipids is rare
fluidity is enhanced by unsaturated hydrocarbon tails of phospholipids
cholesterol molecules reduce fluidity but help prevent solidification at low temperatures by preventing tight packing of phospholipids

5. Membrane Proteins
mosaic – collage of different proteins embedded in the fluid matrix of the lipid bilayer
integral proteins – penetrate the hydrophobic core of the lipid bilayer; many are transmembrane
peripheral proteins – bound to the surface of the membrane
proteins determine most of the membrane’s specific functions

6. Membrane Protein Functions

7. Glycoproteins & Glycolipids
carbohydrates attached to membrane proteins & lipids
function as “name-tags” to help distinguish cells (cell-cell recognition)
important in sorting cells into tissues & organs during embryonic development
basis for rejection of foreign cells

8. Membrane Synthesis begins in ER vesicles fuse with plasma membrane
the inside layer of the vesicle becomes the outside layer of the cell

9. Form Fits Function
the plasma membrane controls traffic into and out of the cell
exhibits selective permeability – allows some substances to cross more easily than other
the fluid mosaic model explains how the plasma membrane is able to do this