Contents of the Membrane

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  • Content of the membrane
    • Phospholipid - form the phospholipid bilayer
      • Hydrophilic phosphate head on the outside of the bilayer; faces the cytoplasm or outside of the cell
        • Stop ions and large permeable molecules from passing through by being impermeable to them
        • Are permeable to non-polar molecules such as fatty acids and oxygen
        • Are permebale to polar molecules such as carbon dioxide, watser and alcohol
      • Hydrophobic hydrocarbon tail which faces the inside of the bilayer
        • Allow movement so that vesicles can move and rejoin
        • From a barrier for water-based substances between the cytoplasm and extracellular fluid
    • Proteins
      • Extrinsic proteins which are on one side of the bilayer only
        • Act as enzymes in some membranes
      • Intrinsic proteins which span the whole bilayer
        • Act as channel and carrier molecules
        • Act as receptors for chemicals such as hormones
    • Cholesterol
      • Are found only in eukaryotic cells
        • Helps to stabilise the membrane by making the head and tail of the phospholipid bind together
        • Reduces permeability to water and non-polar molecules
        • Stops the phospholipids from solidifying at low temperatures and becoming too fluid at high temperatures
    • Carbohydrates
      • Form glycoproteins when joined with proteins
        • Allow cell adhesion by making the cells in a tissue stick together
      • Form glycolipids when joined with phospholipids
        • Allow cell signalling by acting as a receptor
        • Act as a recognition site for cells such as leucocytes

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