Biology 180 Chapter 6

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Author:
rosylyn
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200910
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Biology 180 Chapter 6
Updated:
2013-02-16 04:56:44
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Chapter 6 Notes
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  1. Plasma Membrane Function
    • • Surrounds all cells
    •   – 8 nm thick (1 nanometer = 10-9 meter)
    • • Separates cell from its environment
    • • Allows SELECTIVE passage of molecules into and out of the cell
    • • Controls flow of materials into and out of the cells
    •     -Allows cell to exchange information with itsenvironment
  2. Plasma Membrane Components
    • • Lipids
    • – Phospholipids
    •    • Bilayer
    • – Glycolipids
    •    • Lipids that contain an attached short branched carbohydrate chain
    • – Cholesterol

    • • Proteins
    •    – Transmembrane proteins
    •       • Proteins that span the membrane– Peripheral proteins
    •      • Proteins that are loosely bound to the membrane surface

    – Most of the proteins exposed on the outside surface of the cell are glycoproteins- protein with short branched carbohydrate chains
  3. Plasma membrane composition
    • • 50% protein & 50% lipid (by weight)
    • – More lipids because they are smaller
    • – 109 (1 billion) lipids/cell
    • – 106 (1 million) lipids/micoM2

    • • The outer face (leaflet) of the bilayer and the inner face (leaflet) of the bilayer do not have the same lipid composition
    • • The composition of the plasma membrane varies between cell types
  4. The Fluid Mosaic Model
    • • The membrane is held together by hydrophobic interactions and van der Waals forces
    •   – Hydrophobic interaction- water molecules exclude nonpolar substances

    • • Lipids move laterally in the membrane
    • – Exchange lateral locations about 107 times/sec
    • – Can travel 2microM/sec
    • – Lipids cannot flip flop between leaflets unless helped by proteins called flipases
    • • Proteins move laterally in the membrane
    •   – Move slower
  5. Membrane proteins can move
    • Plasma membrane proteins of a mouse cell was labelled with a fluorescent molecules

    • Plasma membrane protein of a human cell was labeled with a different color of fluoresenct molecules

    • The membranes were experimentally forced to fuse

    • Result was that proteins freely diffused
  6. What affects membrane fluidity?
    • • Temperature
    •     – Increase of temperature increases membrane fluidity
    • • Saturation of phospholipid fatty acids
    •    – decrease in saturation increases membrane fluidity
    • • Length of Fatty acid
    •    – Decrease in length increases membrane fluidity
    • • Cholesterol
    •    – Can make membrane stiffer or more fluid depending on lipid composition and temperature.
    •    – Can prevent membrane crystallization at low temperature (lobsters have high cholesterol)
  7. Cells can change plasma membrane lipid saturation
    • • Desaturate single bonds to double bonds in the fatty acids
    •    – Done by enzymes called desaturases

    • • Shuffle the fatty acids so lipids have 2unsaturated fatty acids
    •    – Phopholipases- clip off fatty acid to be moved
    •    – Acyltransferases- trasfers the clipped fatty acid to a different phospholipid
  8. Types of membrane proteins
    • • Transmembraneproteins
    •    – Proteins that span the membrane
    •    – Also called integral membrane proteins

    • • Peripheral membrane proteins
    •    – Proteins that are loosely bound to the membranes surface

    Modified from image found at:
  9. Transmembrane proteins

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