1.5 lipids

• The main groups of lipids are triglycerides and phospholipids
• Triglycerides have three fatty acids combined with glycerol
• In a triglyceride, each fatty acid forms an ester bond with glycerol in a condensation reaction
• Hydrolysis of a triglyceride produces glycerol and three fatty acids
• glycerol + 3 fatty acids —> triglyceride + 3 H2O
• All fatty acids have a carboxyl (-COOH) group with a hydrocarbon group attached
• If a fatty acid doesn’t have a double carbon bond, it is described as saturated.
• If a fatty acid has a single double-bond, it is described as mono-unsaturated
• If a fatty acid has more than one double-bond present, it is described as polyunsaturated.
• Phospholipids are similar to lipids except one of the fatty acid molecules is replaced by a phosphate molecule
• Fatty acids are hydrophobic whereas phosphates are hydrophilic
• A phospholipid has a hydrophilic head, and a hydrophobic tail
• test for lipids:

  1. add sample and 5cm of ethanol
  2. shake the tube
  3. add 5cm of water and shake gently
  4. a milky-white emulsion is a positive result