Lipids

• What is a Triglyceride?


  A type of fat molecule made of a glycerol backbone and 3 fatty acids.
• What is the general formula for fatty acids?


  R-COOH
• Describe how to test for lipids in a sample.

  1. Dissolve solid samples in ethanol
  2. Add an equal volume of water and shake
  3. Positive result= milky white emulsion.
• How do triglycerides form?

  Condensation reaction between 1 molecule of glycerol and 3 fatty acids form ester bonds.
• Difference between saturated and unsaturated fatty acids

  • Saturated contain single bonds only whereas unsaturated contain C=C double bonds
  • Saturated have straight chain molecules which have many contact points whereas unsaturated have 'kinked' molecules which have fewer contact points
  • Saturated have higher melting points so are solid at room temp whereas unsaturated has a lower melting point and are liquid at room temp.
  • Saturated are found in animal fats whereas unsaturated fats are found in plant oils.
• Relate the structure of triglycerides to their functions

  • High energy: mass ratio= high calorific value from oxidation
  • Insoluble hydrocarbon chain+ no effect on water potential of cells and used for waterproofing.
  • Slow conductor of heat= thermal insulation
  • Less dense then water= gives buoyancy to aquatic animals.
• Describe the structure of phospholipids

  Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head.

  • Forms phospholipid bilayer in water
  • Tails can splay outwards= waterproofing
• Similarities of phospholipids and triglycerides

  • Both have glycerol backbone
  • Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids.
  • Both contain C, H, O
  • Both formed by condensation.
• Differences between phospholipids and triglycerides

  • Phos have 2 fatty acids and 1 phosphate group attached whereas trigly have 3 fatty acids attached
  • Phos are hydrophilic at the head whereas the tail is hydrophobic whereas in trigly the whole molecule is hydrophobic.
  • Phos are used mainly in membrane formation whereas trigly are primarily used as a storage molecule.
• Are phospholipids and triglycerides polymers?

  No, they are macromolecules.