Lipids

Biology Essay Ð'- Lipids

Lipids are a big group of organic compounds. They are made up of Carbon, Hydrogen and Oxygen; though there is a lot less oxygen in lipids than there is in carbohydrates.

Triglycerides are the most common lipid. They are made up of 3 fatty acid chains attached to a glycerol molecule linked together by ester bonds. The fatty acid chains and glycerol molecules join together during 3 condensation reactions. 3 water molecules are formed as a result.

Fatty acids are hydrocarbon chains connected to a carboxylic group (COOH). If every carbon atom in the chain is linked together by a single bond, the fatty acid is saturated. Therefore, they are solids at room temperature and are mostly found in animals. Saturated fats are more readily converted to cholesterol. Examples are butter, chocolate and cheese.

If one or more bonds between the carbon atoms is a double bond, we say the lipid is unsaturated. These hydrocarbon chains are shorter than the saturated chains and are soft fats or oils at room temperature. Most plant fats are unsaturated.

Triglycerides are non-polar and therefore insoluble in water. They are compact long term energy stores. When oxidised, triglycerides release twice as much energy for respiration as carbohydrates. They therefore also release twice as much water (metabolic water). This is very important in the development of young birds and reptiles.

These lipids also aid buoyancy and act as additional layers of fat for thermal insulation for hibernating animals. In plants, the waxy cuticle prevents excess evaporation from the surface of the leaf.

Phospholipids have only a glycerol molecule, 2 fatty acid groups as a phosphate group replaces one of them. This is important in membrane structure as a source of acetylcholine and in the transport of fat between