Structure of cell surface membrane

• Fluid mosaic model

  • Molecules within phospholipid bilayer can move relative to one another causing it to be more flexible and change shape
  • Proteins embedded in bilayer can vary in shape, size and pattern
• Phospholipid bilayer


  All molecules arranged within creating a partially permeable membrane forming the cell surface membrane
• Phospholipid bilayer

  • Hydrophilic heads which attract water molecules
  • Hydrophobic tails are fatty acid chains with NO charge, they will repel water but attract other lipids
• Cholesterol

  • Embedded in phospholipid bilayer, binds to hydrophobic tail which packs them closely together
  • Restricts lateral movement of molecules, maintains stability
  • Useful as at higher temperatures it makes membrane less fluid preventing water and dissolved ions leaking out of the cell
• Proteins embedded across cell surface membrane

  • Peripheral proteins (does not extend completely across membrane)
  • Integral proteins: Channel proteins, Carrier proteins
• Peripheral proteins

  • Provides mechanical support
  • Carbohydrate chains attached to form glycoproteins
• Channel proteins

  Form tubes that fill with water allowing water soluble ions to diffuse
• Carrier proteins

  Binds with other larger molecules e.g glucose and amino acids which change shape to transport them to the other side of the membrane
• Glycolipids


  • Carbohydrate and lipids covalently bonds
  • Glycolipid receptor act as recognition sites for cells to recognise each other
  • Helps with cell to cell adhesion
  • Maintains stability
• Glycoproteins

  • Carbohydrate attached to protein
  • Receptor for hormones and drugs
  • Helps cell to cell adhesion
  • Acts as recognition site
• Only lipid soluble and small (CO2, H2O, O2) can simply diffuse through the membrane
• Water soluble (Polar) molecules cannot diffuse through the membrane
• Molecule must be oppositely charged to protein channel or will be repelled to pass through the membrane
• It is difficult for polar molecules to pass through the membrane as they have to pass through non polar hydrophobic tails