lipids

• Lipids= molecules containing carbon, hydrogen and oxygen.
• Lipids are non-polar molecules. This means there are no positive or negative areas within the molecules and so lipids are not soluble in water.
• Lipids are large complex molecules known as macromolecules which are not built from repeating units.
• Triglyceride= one glycerol molecule and three fatty acids (1 glycerol + 3 fatty acids)
• Both the glycerol and fatty acids have hydroxyl groups which interact, leading to the formation of three water molecules and bonds between the fatty acids and the glycerol molecule- ester bonds.
• The bonds in a triglyceride are called ester bonds and the reaction is called esterification. Esterification is another example of a condensation reaction.
• Fatty acid chains that have no double bonds between the carbon atoms are called saturated, because all the carbon atoms form the maximum number of bonds with hydrogen atoms.
• If one double bond is present in a fatty acid it is called monounsaturated. If more than one double bond is present it is called polyunsaturated.
• The presence of double bonds causes kinks or bends and therefore the molecule cannot pack so closely together. This makes them liquids at room temperature (therefore they are described as oils rather than fats).
• Phospholipids are modified triglycerides and contain phosphorus as well as carbon, hydrogen and oxygen.
• One of the fatty acid chains in a triglyceride molecule is replaced with a phosphate group to make a phospholipid.
• Phospholipids have hydrophobic tails and a hydrophilic phosphate head.
• Phospholipids are called surface active agents because they will form a layer on the surface of the water with their phosphate heads in the water and their hydrophobic tails sticking out of the water.
• Phospholipids also form bilayers with all of their hydrophobic tails pointing towards the centre protected from the water by their heads.
• Roles of lipids:

  • membrane formation
  • hormone production
  • electrical insulation
  • waterproofing
  • thermal insulation
  • buoyancy
• Lipids can be identified by the emulsion test. The sample is mixed with ethanol, then the resulting solution is mixed with water and shaken. If a white emulsion forms this indicates the presence of a lipid.