Answer: Fatty acids are fats that have acidic carboxyl groups on them. Something like CH3-(CH2)n-COOH Unsaturated fatty acids have double bonds between 1 or more of the carbons in the chain. They are unsaturated with hydrogen, but can be hydrogenated chemically. Fatty acids have many roles, but a very common one is to form the lipids in membranes. In that case two fatty acids are usually joined to phosphate plus some others.