membrane structure

• 1. hydrophilic head
  2. hydrophobic tail
  3. phosphate
  4. glycerol
  5. saturated fatty acid
  6. unsaturated fatty acid

  
• phospholipid

  
• Phospholipid Bilayer - This bilayer acts as a barrier to most water-soluble substances and prevents leaking of water-soluble molecules. The tails are joined together by Van de Vaals forces.

  
  

  The heads are joined to the water molecules in solution by hydrogen bonding.

  
  

  Because the outside and inside of cells are aqueous and the bonds holding the bilayer together relatively weak it means the bi-layer is flexible.

  
• Fluid Mosaic Model - Phospholipids are “fluid”- they are free to move within the layer leading to membrane flexibility. The proteins are variable in size and shape  and are scattered randomly throughout the membrane like tiles within a mosaic

  
• intrinsic proteins -

  • Transmembrane- embedded in both layers of the membrane
  • Examples: channel proteins, carrier proteins, glycoproteins
• extrinsic -

  • Found on the surface/present on one side of the bilayer
  • Usually function as enzymes and catalyse chemical reactions e.g. hormones
• • Channel proteins provide a hydrophilic channel.
  • This allows small polar molecules and ions to pass passively through the membrane.
  • Movement is down a concentration gradient

  
• • Carrier proteins can change their shape in order to transport molecules across the membrane.
  • They can be used in both passive and active transport.

  
• glycoproteins - Intrinsic proteins with carbohydrate chains attached

  • Play a role in cell adhesion in certain tissues
  • Important for communication- act as receptors for chemical signals
  • Process called cell signalling

  
• cholesterol -

  • Regulates the fluidity of the membrane and adds stability
  • Lipids with a hydrophilic head and a hydrophobic tail. Positioned between phospholipids in the bilayer

  
• glycolipids -

  • Lipids with attached carbohydrate chain
  • Glycolipids act as cell markers or antigens for cell-cell recognition
  • Recognised by the immune system