Lipids

• Fatty acids are made up of a hydrocarbon chain that is attached to a carboxyl group (RCOOH)
• Triglycerides are made from one glycerol molecule and three fatty acids
• Fatty acid is hydrophobic making lipids insoluble in water
• Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.
• A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.
• The R-group of a fatty acid may be saturated or unsaturated.
• saturated fatty acid don't have double bonds between their carbon atoms
• unsaturated fatty acids have double bonds within the carbon chain, which makes them more fluid.
• Properties of triglycerides

  • Energy store - large ratio of carbon-hydrogen bonds compared to number of carbon atoms so a lot of energy is stored
  • Metabolic water source - high ratio of hydrogen to oxygen so can release water if they are oxidised
  • Not affect water potential - large and hydrophobic making the insoluble
  • Low mass - stored without increasing the mass
• In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
• Properties of phospholipids

  • Hydrophilic head attracts water
  • fatty acid tail repels water
  • have 2 charged regions so are polar
  • forms phospholipid bilayer membrane with head facing towards water and tail facing away
• Emulsion test for lipids

  • Add ethanol
  • add water and shake
  • White/milky emulsion