Lipids are a diverse group of organic compounds that include triglycerides, phospholipids, waxes, cholesterol, and steroids. They are non-polar and do not dissolve in water. Triglycerides are a common type of lipid composed of a glycerol molecule bonded through ester bonds to three fatty acid molecules. Lipids serve several important functions in living things including long-term energy storage in tissues like adipose and plant oils, buoyancy for marine animals, insulation beneath skin, and production of metabolic water during respiration.

1.  Lipids: a large and varied group of organic compounds.  Lipids include: Triglycerides Phospholipids Waxes Cholesterol and Steroids  Lipids are all non-polar and do not dissolve in water

2.  Triglycerides are one of the most common types of lipids  Triglycerides consist of one molecule of glycerol bonded to three fatty acid molecules  Each fatty acid is linked to the glycerol molecule by an ester bond C C C H OH H H H H OH OH Glycerol Hydroxyl groups

3. Fatty Acids: General Formula: CH 3 (CH 2 ) n C O OH Carboxyl group H C C C H H H H H H C C C H H H H H H C O OH CH 3 CH 2

4. Can be drawn as: H C C C H H H H H H C C C H H H H H H C O OH C O OH

5. Forming a monoglyceride: + H 2 O This is a condensation reaction C C C H OH H H H H OH O H C O OH C C C H OH H H H H OH O C O Ester bond Hydroxyl group and carboxyl group react

6. A triglyceride: Can be drawn as: C C C H O H H H H O O C O C O C O Glycerol Fatty acid Fatty acid Fatty acid Ester bond

7. To split these ester bonds and separate a fatty acid from glycerol we need to add a molecule of water + H 2 O This is a hydrolysis reaction C C C H OH H H H H OH O C O C C C H OH H H H H OH O H C O OH

8. Uses of Lipids in Living Things 1. Long-term energy stores Human Adipose Tissue Plant Oils

9. 2. Buoyancy for marine animals: lipids are less dense than water so help animals float 3. Insulation: a layer of fat beneath the skin cuts down heat loss

10. 4. Production of water: fatty acids produce a lot of metabolic water when they are oxidised during respiration Camels’ humps are made of fat e.g. C 17 H 35 COOH + 26 O 2  18 CO 2 + 18 H 2 O (a typical fatty acid)

11. Homework : Compare the relative advantages and disadvantages to an organism of using carbohydrates and lipids as energy stores To be handed in on a separate sheet of paper.