Arachadonic acid is a carboxylic acid with a 20 carbon chain and four cis-double bonds. They do not have any functional groups. It is a polyunsaturated fatty acid present in the phospholipids of the membranes in the cells of the body, brain, muscle and liver. Prostaglandins are the active lipids compounds abundant in human tissue. They are a 20 carbon chain saturated fatty acids with a 5 carbon ring forming a cyclopentane. It has one trans-double bond, two hydroxyl functional groups and a ketone functional group.