Lipids refers to a group of compounds such as fats, oils, phospholipids and steroids. Lipids contain Carbon, Hydrogen and Oxygen. It must be noted that lipids are in-soluble in water.

Simple lipids

fats and oils are known as triglycerides since their molecular structure consists of glycerol combined with three fatty acids as shown below:

These are slightly different, they contain two fatty acids linked to a phosphate group. The phosphate (or head) is hydrophilic where as the fatty acids are hydrophobic.


Steroids - These are slightly different lipids, they are composed of three 6-carbon rings attached to a single 5-carbon ring. An example of a steroid would be cholesterol or sex hormones.

Roles of Lipids
  • Energy Store - fat is held in adipose tissue, it is insoluble in water and structurally compact, which makes it an effective energy store. When fat is required it can be broken down into glycerol and fatty acids, it is then used as a respiratory substrate.
  • Thermal and Nerve Insulation - Fat helps stop body heat being lost. It also produces a myelin sheath around each nerve, which increases the speed of the transmission of the signal.
  • Fat pads are located in the balls of the feet and the palms of the hands, they help protect bones by acting as cushions.
  • They also play a part in vitamin transport - vitamins A,D,E and K are all fat-soluble, they are incorporated into micelles which is then transported in the lymphatic system
  • As we will find out later lipids play a major role in cells membrane.