Glycerophospholipids and fatty acids in mitochondrial membranes. (A) Phospholipid molecules are composed of a glycerol backbone to which are attached (sn-1 and sn-2 hydroxyl groups) fatty acid chains of variable length and number of double bonds. A hydrophilic head group can be attached via a phosphodiester bond formed at the sn-3 position. (B) The first carbon in carboxylic acids is at the alpha end. The last carbon is at the omega (n) end. For omega-3 (n-3) fatty acids, such as docosahexaenoic acid, the first double bond is three carbons from the omega end. The first double bond for omega-6 (n-6) fatty acids, such as linoleic acid, is at the sixth carbon from the omega end. Examples of nomenclature are shown: the carbon chain length beginning from the alpha end is shown in blue. The carbon double bonds are shown in green. The position of the first carbon double bond from the omega end is shown in red.