Fatty acids are made up of a chain of carbon atoms, with a methyl group (-CH3)
at one end and a carboxylic acid group (-COOH) at the other. To each
carbon atom in the chain one or two hydrogen atoms are attached. (See
images below). If all the carbons in the chain are attached to 2
hydrogens, the chain has only single bonds, and is called saturated.
If some of the carbon atoms in the chain are attached to only one hydrogen, double bonds to the neighbouring carbon atoms form, and the fatty acid is called unsaturated.
If there is just one double bond in a fatty acid, it is called monounsaturated. If it consists of multiple double bonds, it is polyunsaturated.
