1. Introduction  Lipids have a varied structure but all have the following properties in common:-  Insoluble in water  Soluble in organic solvents  The three main groups of lipids are:-  Triglycerides  Phospholipids  Steroids  Lipids are important in cell membrane structure and also as energy storage molecules and hormones.

2. Triglycerides  Triglycerides consist of a single glycerol molecule and three fatty acids. Glycerol Fatty acids

3. Formation of Triglycerides  Triglycerides form by condensation (dehydration) reactions between the hydroxyl (OH) groups of the glycerol and the carboxyl (COOH) group of three fatty acids.  Triglycerides are esters being derived from an alcohol and a fat.

4. Triglycerides (cont’d.)  Glycerol (blue) is an alcohol derivative of glyceraldehyde and has three hydroxyl groups. It acts as the backbone of the structure.  Fatty acids (red) – there are more than 70 types of fatty acid but they all have long hydrocarbon tails and a terminal carboxyl group (COOH). The variety of fatty acids determine the properties of each triglyceride.

5.  The structure of triglycerides is varied due to the variety of fatty acids. These molecules may be two types which give rise to lipids with different properties:-  Saturated – these have no double C - C bonds e.g. palmitic acid and stearic acid. Triglycerides containing saturated fatty acids are very straight in structure and pack closely together.  Unsaturated – have one or more double C - C bonds e.g. oleic acid or linoleic acid. Lipids containing unsaturated fatty acids are ‘kinked’ in structure and cannot pack so closely together. Structure of Triglycerides

6. Triglycerides in Animals  Animals store their energy in triglycerides with high melting points which are solid at room temperature.  These triglycerides are referred to as fats. result from reaction between glycerol and a saturated fatty acid e.g. stearic acid.

7. Triglycerides in Animals Tips to help you remember. In animals triglycerides contain :  S ingle bonds only in fatty acids  S aturated fatty acids  S traight chained fatty acids  S tearic Acid is an example  S olid at room temperature – high melting point  S tore energy  Source of metabolic water  S imply amazing as insulation and buoyancy aid

8. Triglycerides in Plants  Plants store their energy in triglycerides with low melting points which are liquid at room temperature.  These triglycerides are referred to as oils result from reaction between glycerol and an unsaturated fatty acid e.g. oleic acid.

9. Triglycerides in Plants Tips - to help you remember. In plants triglycerides are the ‘opposite of animals’ so learn the animals first and then go through the list and change as follows  Double bonds in fatty acids  Unsaturated  Kinked chains  Oleic Acid is example  Liquid at room temperature – low melting point  S tore energy

10. Triglycerides in Cells  Triglycerides are insoluble in water because they have no charge i.e. they have covalent bonds. This causes them to form droplets in the cytoplasm.

11.  Energy storage - triglycerides contain twice the energy/gram of carbohydrates or proteins. During aerobic respiration triglyceride is broken into 2C portions which are fed into the Krebs cycle. Functions of Triglycerides  Source of metabolic water – water is released on the breakdown of triglycerides and this property is used efficiently is by desert mammals.

12. Functions of Triglycerides (cont’d.)  Insulation – triglycerides are found in the blubber of whales and other aquatic animals.  Buoyancy – aquatic animals use triglycerides to help them float as they are less dense than water.