Chapter 7 BIO 117 Notes.docx

Chapter 7 BIO 117 Notes.docx - PlasmaMembrane...

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Plasma Membrane   Cell membranes are Selectively Permeable-  Allow some substances to cross  easier than others   Phospholipids structure allow for the membrane to function  Amphipathic - Has a hydrophilic  and Hydrophobic region, i.e.  phospholipids  Other types of membrane molecules can also be amphipathic, membrane  proteins are mostly amphipathic with hydrophobic portions sheltered and  hydrophilic portions happy   Membranes are fluid  mosaics  Phospholipids switch places side to side (laterally) only . at 10^7 times per  second   Proteins can move laterally but cannot flip like phospholipids cant either  Lipids and proteins can shift sideways like elbowing through a party  Fluid Mosaic Model    Membrane is Fluid due to weak hydrophobic interactions  Water, glucose and hydrogen ions are examples of things that cannot pass  rapidly through the membrane  Proteins are varied in form and functions and form the Mosaic   Some membrane proteins drift among the membrane and some are static  dependent on the attachments to transport proteins or the extra cellular matrix  Membrane remains fluid with temperature changes as long as the lipids do  not solidify like grease in a bacon pan  Temperature at which a membrane solidifies depends on the lipids  composing it   Membranes that have many unsaturated hydrocarbon phospholipid tails  maintain fluidity as temperature decreases   Number of unsaturated tail compounds in a membrane correspond with the  fluidity response to temperature  Cholesterol is a fluidity buffer mostly found in animals (plants use related  steroid lipids)  As fluidity increases cholesterol restrains movement of phospholipids and as temperature decreases cholesterol hinders close packing of phospholipids  Fluidity must be just right to work with enzymes and functions in the  permeability    
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  Membrane Structure   Variations in lipid composition are important to evolution  By making hydrocarbon tails shorter you can increase fluidity   Organism in extreme cold or heat have been observed to have more  unsaturated hydrocarbons   Some  organisms can change their membrane composition such as Bacteria  and Archaea  Membrane Proteins   2 Major types of membrane proteins are Integral and Peripheral  Integral- Permeates hydrophobic inter portion of membrane, Hydrophobic  regions are composed of structures of non polar amino acids (20-30) usually  alpha helices 
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