Transport across the Membrane

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  • Created by: penny.ee
  • Created on: 26-04-17 13:49
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  • Membrane Transport
    • Phospholipid Bilayer
      • Fluid Mosaic - as phospholipids are able to move laterally to one another/swap places. Mosaic refers to the arrangement of phospholipids and proteins
      • consists of a bilayer of hydrophobic fatty acid tail and hydrophyllic phosphate head
      • includes; intrinsic/ extrinsic proteins, peripheral protein etc.
    • Simple Diffusion
      • The passive, net movement of molecules/ ions from an area of high con. to low con. until they are evenly distributed
      • Factors Affecting
        • Temperature: as temp. increases, so does the amount of kinetic energy = faster diffusion rate
        • Conc. Gradient: The greater the difference on either side of the diffusion pathway, the greater the rate
        • Surface Area: larger surface area = faster rate
        • Diffusion pathway: short = faster rate
    • Facilitated Diffusion
      • Carrier Proteins
        • 1) Molecules bind to binding sites within the protein from the area of high conc.
        • 2) Molecules are then released across the membrane from the binding sites
      • Channel Proteins
        • Transport small, polar molecules e.g. ions
        • The channel pore is charged to guide the ions (each channel is specific to the ion)
    • Active Transport
      • The active, net movement of molecules/ ions into/out of a cell against a concentration gradient
      • The process requires ATP and is used in: protein synthesis, muscle contraction, neurotrans-missions and mineral absorption
      • It uses carrier proteins with specific binding sites and only take complement-ary molecules
        • CO TRANSPORT - an indirect form of active transport e.g. Sodium/ Potassium pump
          • Actively transports Na+ out of the blood and K+ into the cell
          • The carrier protein transports glucose down the conc. gradient
          • The co-transport protein transports Na+ down the conc. gradient and glucose against the conc. gradient
    • Osmosis
      • Passage of water from a solution of high water potential to a solution of low water potential through a partially permeable membrane
      • HYPERtonic
        • Water potential is lower on the outside
        • Water leaves the cell and becomes flaccid
        • Pressure falls
      • HYPOtonic
        • Water potential is higher outside
        • Water enters the cell and becomes turgid
        • Pressure rises
      • Low WP = more negative (less free water molecules = conc. solution)
      • Isotonic Solution - if solution has the same water potential both in and out of the cell
      • Water Potential - the pressure created by the water molecules trying to diffuse out of a solution down a gradient

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