cell membrane

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  • Transport Across Cell Membranes
    • Roles of membranes
      • Too large to pass through channels
      • Molecules that are not soluble in lipids so can't pass through the phospholipid bilayer
      • Polar molecules
      • To act as partially (and sometimes selectively) permeable membranes between
      • Same charge as protein channels to repel each other.
    • Membrane Structure
      • Fluid Mosaic Model-
        • (Fluid) phospholipids and are continually moving relative to each other
        • (Mosaic) Membrane is constructed from several different components including phospholipids proteins, and modified proteins
    • Membrane Components
      • Cholesterol
        • Has hydrophobic regions-create further barrier to polar substances moving through the membrane
        • Membrane stability
          • Reduces lateral movement of phospholipids
        • Type of lipid.
        • Embedded between fatty acid tails of phospholipids
      • Proteins
        • Channel proteins
          • Allow water soluble molecules to pass through membrane
        • Intrinsic
          • span the entire membrane
            • Some intrinsic Proteins are channel Proteins
        • Extrinsic
          • embedded in one half of the membrane
        • Carrier
        • Helps cells adhere together
          • Provide structural support
            • Acts as receptors e.g. hormones
      • carbohydrates polymers
        • When carbohydrate polymers attach covalently to proteins to form glycoproteins
        • Carbohydrate chains may attach covalently to extrinsic proteins  forming glycolipids.
          • Glycolipids
            • Helps cells attach to each other to form tissue
            • Act as recognising sites
            • Helps maintain stability of the membrane.
        • Glycolipids & glycoproteins
          • Act as receptors for drugs, antibodies and hormones to bind
  • Glycopoteins
    • Covalently boned to proteins
    • Cell surface receptors for signalling molecule hormones
    • Helps cells attach to each other to form tissue
    • Allows cells to recognise each other for the immune system
    • When carbohydrate polymers attach covalently to proteins to form glycoproteins
  • carbohydrates polymers
    • Carbohydrate chains may attach covalently to extrinsic proteins  forming glycolipids.
      • Glycolipids
        • Helps cells attach to each other to form tissue
        • Act as recognising sites
        • Helps maintain stability of the membrane.
    • Glycolipids & glycoproteins
      • Act as receptors for drugs, antibodies and hormones to bind
  • Transport Proteins
    • allow the movement of molecules that are normally too large or too Hydrophilic to pass through the membrane
    • tube-like structure that goes through the whole membrane.
    • Other transport proteins are carrier proteins.
    • Proteins
      • Channel proteins
        • Allow water soluble molecules to pass through membrane
      • Intrinsic
        • span the entire membrane
          • Some intrinsic Proteins are channel Proteins
      • Extrinsic
        • embedded in one half of the membrane
      • Carrier
      • Helps cells adhere together
        • Provide structural support
          • Acts as receptors e.g. hormones
  • Membrane channels proteins in the plasma membrane that allow water through
    • Aquaporins
    • Since water is polar aquaporins are needed

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