*Membrane Structure and Function
*Selective permeability- allows some substances to cross it more easily than others
*Phospholipids are the most abundant lipids in membranes
*An amphipathic molecule (has both hydrophilic and hydrophobic region), proteins too
*Overton hypothesized that membranes are made of lipids
*Langmuir made artificial membranes by adding phospholipids dissolved in benzene to water
*Benzene evaporated, phospholipids remained as a film covering the surface of water with only the hydrophilic heads immersed in the water
*Gorter | Grendel reasoned that cell membranes were two molecules thick (bilayers)
*Davson | Danielli proposed the model of a bilayer sandwiched between two layers of protein
*Singer | Nicolson proposed that proteins are dispersed and individually inserted into the bilayer
*Fluid mosaic model- the membrane is a fluid structure with various proteins embedded in or attached to a bilayer of phospholipids
*Freeze-fracture prepares cells for electron microscopy
*Splits a membrane along the middle of the phospholipids bilayer into a P face and E face
*Etching enhances the topography (removal of frozen water by direct evaporation; sublimation)
*A mist of platinum is sprayed on the fracture surface of the cell with a coat of carbon for strength
*The original specimen is digested away
*The replica is examined through the electron microscope
*Membranes are fluid, held together primarily by hydrophobic interactions
*Lateral movement of phospholipids within the membrane is rapid
*Flip-flopping across the membrane is rare
*Membrane remains fluid as temperature decreases until the phospholipids settle into a closely packed arrangement and the membrane solidifies; temperature of solidification depends on the types of lipids it is made of; membranes remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails
*Cholesterol at body temperature in humans makes the membrane less fluid by restraining the movement of phospholipids; lowers...
Deutsch: Schematische Darstellung der Diffusionsvo...
Cell Membrane
English: Yeast cell membrane visualized by some me...