Compounds that contain a fused ring system are called these have three 6-membered rings and one 5-membered ring. some of these compounds are found in biological membranes. are the building blocks for many lipids, and they generally contain an even number of carbon atoms and an unbranched hydrocarbon chain. are formed when a carbohydrate is glycosidically linked to a hydroxyl group of a lipid. examples include gangliosides and cerebrosides. these are also found in biological membranes. are the storage form of lipids, accumulating in adipose tissue, and they can be metabolic fuel. these compounds have a polar part, made of three ester groups, and a nonpolar fatty acid tall. made of a long-chain amino alcohol joined, either by a glycositic linkage or a phosphodiester linkage, to a fatty acid. these do not contain they are abundant in the nervous system. when glycerol is esterified to two fatty acids and a phosphoric acid molecule a is formed. these are found in biological membranes.