Glucose is the primary fuel for most cells and the nearly exclusive fuel for most nervous system cells. Anerobic muscle fibers (those important for strength and speed) depend mostly upon glucose and store glycogen for rapid hydrolysis to glucose. Glycogen is also stored in the liver.
	The carbohydrate portions of glycoproteins and glycolipids are part of the glycocalyx or "sugar coating" many cells have. This layer is part of the recognition system by which cells are identified by other cells such as those of the immune system, and it functions as a protective coating for some cells. Proteoglycans are molecules with a core protein and attached glycosaminoglycans (GAGs). See [The Structure of a Proteoglycan Complex]. GAGs are composed of aminated (containing amine groups) and sulfated (containing sulfate groups) disaccharides and are important to the structure and function of many tissues and the extracellular matrix (ECM). [See histology ]. Glycosaminoglycans include hyaluronic acid, heparan sulfate (gives rise to heparin), keratan sulfate (gives rise to keratin), glucosamine, and chondroitin sulfate. Other glycoproteins include collagen, elastin, and reticular fibers.