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.