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Lipids:

Lipids:

  • Triglycerides are either fats or oils. They are made from the elements carbon, hydrogen, and oxygen only.
  • They are insoluble in water.
  • Triglycerides are used for:
  1. Long term energy storage molecules
  2. Insulation
  3. Protection (pericardium)
  4. Buoyancy
  5. Synthesis of specific hormones (steroids)

 

  • Triglycerides are formed in condensation reactions between 1 glycerol and 3 fatty acids.
  • An ester bond forms between the fatty acid and the glycerol.
  • Saturated fatty acids contain the maximum number of hydrogen atoms and no carbon-carbon double bonds. They are found in animal fats and dairy products.
  • Monounsaturated fats contain 1 double bond, for example olive oil.
  • Polyunsaturated fats contain a larger number of double bonds, for example, vegetables and fish oils.
  • If one of the fatty acids in a triglyceride is replaced with a phosphate group, a phospholipid is formed. These molecules make up part of the cell membrane.
  • Cholesterol is a short lipid molecule with a structure very different to a triglyceride. It is important for cell membranes, sex hormones, and bile salts. Found in food, associated with saturated fats.
  • The C=C bonds form ‘kinks’ in the fatty acid chains, pushing adjacent triglycerides away from each other. This lowers the effect of intermolecular forces, lowering the boiling and melting temperatures.

 

  • Tests for triglycerides:
  1. Add ethanol (dissolves fat)
  2. Add water.
  3. A white precipitate indicates a positive result.