Membrane Structure & Function Chapter 7

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

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

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

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

Membrane Protein Functions

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

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

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