Movement of molecules in Cells

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  • Created by: Zoe
  • Created on: 17-05-13 16:54
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  • Movement through Cell Membranes
    • Diffusion
      • movement of molecules from a region of high concentration to a region of low concentration
      • Net Movement:
        • no overall movement of molecules in one direction
      • Rate Factors
        • Larger surface area
        • Temperature
        • thin membrane
        • steep concentrationgradient
      • small or lipid based molecules through the bilayer
    • Facilitated Diffusion
      • diffusion of larger, charged molecules which cannot pass through the bilayer.
      • Two proteins used
        • Carrier Proteins
          • shaped so specific molecules fit into them. Protein changes shape when it does, to allow molecule through to other side of membrane
        • Channel Proteins: form water filled channels across membrane allowing water soluble ions to pass through
    • Osmosis
      • movement of water from a high water potential to a low water potential through a partially permeable membrane
      • In Animal Cells
        • Cells bathed in tissue fluid to avoid haemolysis
      • When water potential is higher
        • water enters cell
      • In Plant Cells
        • Higher Water Potential
          • cell becomes turgid from entering water
        • Equal water potential
          • incipient plasmolysis
        • Negative water potential
          • cell becomes plasmolysed as water leaves cell.
    • Active Transport
      • Movement of molecules from a low to a high concentration  using ATP
      • Carrier proteins (pumps) are complimentary to molecule they cary
        • Carry specific molecules one way using ATP against conc gradient
      • One way Flow:
        • energy used to pump changes shape of protein so molecule can only fit in one way
    • Bulk Transport
      • Endocytosis
        • bringing materials into the cell
        • cytoplasm enclose bacterium, forming a vesicle.
      • Exocytosis
        • moving material out of cell
        • substances are released when vesicular membrane fuses with plasma membrane.
  • bringing materials into the cell


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