Like amylopectin, glycogen is a highly branched polymer of glucose that is the main storage form of carbohydrate in humans. The main chain of the structure is composed of alpha 1, 4 glycosidic bonds, while alpha 1,6 glycosidic bonds give rise to the branch points of the polymer (figure 5). Glycogen is stored in the liver and muscle where it is synthesized and degraded depending upon the energy requirements of the body.
Indigestible forms of polysaccharides are known as dietary fiber and come in many different forms including cellulose, hemicellulose, pectin, gum and mucilage. Cellulose is by far the most abundant biochemical compound on the earth because it forms part of the structure of many plants. It is unique among polysaccharides in that it forms intramolecular hydrogen bonds between adjacent glucose units as well as beta 1,4 glycosidic bonds present in other carbohydrates. These special bonding characteristics allow cellulose to form long, straight chains of glucose and give it strength and rigidity that many plants require for proper growth. Cellulose and most forms of hemicellulose are insoluble fibers while pectin, gum and mucilage are all soluble fibers and readily dissolve or swell when mixed with water.
Other sugars of importance are found in nucleotides such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both RNA and DNA are five sided cyclic sugars; however, RNA has one more hydroxyl group than DNA. Glucose-6-phosphate, an intermediate in the breakdown of glucose for energy, can be used for the synthesis of these compounds.