STRUCTURE OF CELL MEMBRANE

• Phospholipid bilayer


  Hydrophilic phosphate heads point outwards, whilst hydrophobic fatty acid tails point inwards towards each other making the bilayer water repellent.
• What substances can diffuse across the cell surface membrane?

  Small lipid soluble substances.
• What proteins are embedded in the cell surface membrane?

  Channel proteins, carrier proteins, glycoproteins
• What is the purpose of channel proteins?

  allow water-soluble ions to diffuse across the membrane
• What is the purpose of carrier proteins?

  Bind to ions/molecules like glucose, amino acids and change shape in order to move the molecules across the membrane
• What type of transport is used in channel proteins?

  facilitated diffusion
• What type of transport is used in carrier proteins?

  Active transport and facilitated diffusion
• What is the role of cholesterol?

  Add strength to the membrane by:

  • reducing lateral movement of other molecules (phospholipids) by pulling fatty acid tails together
  • makes membrane less fluid at higher temperatures
  • prevent leakage of water and dissolved ions from the cell (as it is very hydrophobic)
• What are functions of glycolipids in the membrane?


  Act as recognition sites, help maintain stability of membrane, help cells attach to one another to form tissues
• What are functions of glycoproteins in the membrane?


  Act as recognition sites, help cells to attach to one another to form tissues, allow cells to recognise one another (e.g. lymphocytes can recognise an organisms own cells)
• What is the fluid-mosaic model of the cell-surface membrane?

  Fluid- as individual phospholipid molecules can move relative to one another making the structure flexible

  mosaic- proteins embedded in membrane vary in shape and size resembling a mosaic