Cell membrane structure

• Why is the cell membrane described as a fluid mosaic model?

  The membranes are described as a fluid-mosaic model due to the mixture and movement of the phospholipids, proteins, cholesterol, glycoproteins and glycolipids it is made of.
• How are the phospholipids in the cell membrane arranged?

  • In a phospholipid bilayer
  • Hydrophilic phosphate heads face outwards towards the water
  • Hydrophobic fatty acid tails face inwards away from the water
• What is the role of cholesterol in the cell membrane?

  • Restricts the lateral movement of other molecules in the membrane.
  • This is useful as it makes the membrane less fluid at high temperatures and prevents water and dissolved ions from leaking out of the cell.
• What is the role of the extrinsic proteins in the cell membrane?

  • Provide mechanical support, as well as carbohydrate chains that are connected to proteins or lipids to make glycoproteins and glycolipids.
  • The function of these is cell recognition, as receptors.
• What is the role of intrinsic proteins in the cell membrane?

  Carrier proteins or channel proteins involved in the transport of a molecule across the membrane.
• Which molecules can pass through the cell membrane?

  • Lipid soluble substances (e.g. some hormones)
  • Very small molecules (e.g. CO , O )
• Which molecules can't pass through the cell membrane?

  • Water-soluble (polar) substances (sodium ions)
  • Large molecules (glucose)