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:
- Long term energy storage molecules
- Insulation
- Protection (pericardium)
- Buoyancy
- 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:
- Add ethanol (dissolves fat)
- Add water.
- A white precipitate indicates a positive result.