Cell membranes

• Phospholipids:

  • form a bilayer
  • hydrophilic heads point outwards and are attracted by water
  • hydrophobic tails point inwards and repel water
• Functions of the phospholipid bilayer:

  • allow lipid-soluble substances to enter and leave the cell
  • prevent water-soluble substances from entering and leaving the cell
  • makes the membrane flexible
• Functions of proteins in the bilayer:

  • structural support
  • some act as channels
  • allow active transport to occur
  • helps cells adhere together
• Channel proteins: allow ions and soluble molecules to cross the membrane
• Carrier proteins: bind to molecules and transport them across the membrane
• Cholesterol:

  • strengthens the membrane
  • hydrophobic so prevent water rloss
  • reduce lateral movement of molecules
• Glycolipids:

  • act as recognition sites
  • help maintain stability
  • help cells attach to each other
• Glycoproteins:

  • act as recognition sites
• Fluid-mosaic model:

  • fluid - flexible structure
  • mosaic - proteins are embedded in the phospholipid bilayer and vary in shape, size and pattern