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Date Submitted: 10/21/2015 11:56 PM
Chapter 7 Biology
Section One
* The plasma membrane exhibits selective permeability; allows some substances to cross it more easily than others
* Plasma membrane and component molecules allow for this selectivity
* Lipids and proteins are main ingredients of membranes; carbs are important too
* Most abundant in lipids is a phospholipid; inherently can make membranes
* Phospholipids are amphipathic molecules; has a hydrophilic region and a hydrophobic region
* Their molecular arrangement allows to shelter hydrophobic tails of the phospholipids from water while the hydrophilic heads are exposed to water
* Fluid mosaic model shows the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
* Membranes are held together with hydrophobic interactions (weaker than covalent bonds)
* Lateral movement within the membrane is rapid; adjacent phospholipids switch positions about 107 times a second
* Proteins move much slower; larger than lipids
* Membrane remains fluid as temp. decreases until phospholipids settle into closely packed arrangement and membrane solidifies
* Temp at which it solidifies depends on lipid it is made of
* Unsaturated hydrocarbon tails cannot pack as closely bc of kinks in the tails where there are double bonds
* UNSATURATED ARE MORE FLUID THAN SATURATED
* Cholesterol (wedged btwn phospholipid molecules) has different effect on membrane fluidity at different temps.
* At higher temps. membrane is less fluid; can lower temp. to solidify “fluidity buffer”
* Membranes must be fluid to work; if it solidifies, permeability changes and enzymatic proteins in membrane become inactive
* Membranes that are too fluid cannot support protein function either: evolution shows differences in membrane lipid composition
* Fish that live in extreme cold have membranes with a high proportion of unsaturated hydrocarbon tails, enabling membranes to be fluid...