April 2010
Written by Sigrid Auweter

Fatty acids are made up of a chain of hydrocarbon (CH2) units that is connected to an acidic carboxyl (COOH) head group.

A fatty acid can be either saturated, or unsaturated. Unsaturated fatty acids contain carbon-carbon double bonds in the hydrocarbon chain. These double bonds create kinks.

The length of the hydrocarbon chain and the degree of saturation determine
the type of fatty acid.

 Fatty acids can have different chain lengths and one or more kinks.

The head group of a fatty acid can react with glycerol. When three fatty acids react with one molecule of glycerol, the resulting molecule is a fat.

The more saturated the fatty acids, the better these fat molecules will be able to “clump” together, creating a rather hard fat. If a fat contains many unsaturated fatty acids, the kinks in the hydrocarbon chains will prevent tight clumping and the fat will be more liquid. Vegetable oils, for instance, contain many unsaturated fatty acids, while animal fats have a higher degree of saturation.

 A fat molecule.


Instead, glycerol can also be linked to only two fatty acids and a phosphate group. Molecules of this class are called phospho-lipids. The phosphate usually connects to another molecule, such as choline.

Phospholipids have a fat loving body (the hydrocarbon chains) and a water loving head. Therefore, when suspended in water, they will form layers, such that the fat loving (hydrophobic) parts cluster together and the water loving (hydrophilic) heads face the water. Hence, when suspended into water, phospho-lipids form membranes.

 Make-up of cellular membranes.
 Membranes consist of two layers of phospholipids, but also contain other
 molecules such as proteins and cholesterol.