Are a major component of all biological membranes and are a class of lipids contaning: fatty acids, a negatively-charged phosphate group, nitrogen containing alcohol and a backbone. Phospholipids with a glycerol backbone are known as glycerophospholipids or phosphoglycerides. The unique phospholipid with a sphingosine backbone is named sphingomyelin. Lipids containing one or more phosphate groups, particularly those derived from either glycerol or sphingosine (sphingolipids). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids.