Polysaccharides are a form of macromolecule that are found in humans, plants, animals and fungi. They are long stands of carbohydrate molecules (glucose) that are bonded together by glycosidic bonds. Polysaccharides usually contain a repeating pattern of the same carbohydrate molecules, and can be both branched and unbranched. Branched polysaccharides are known as amylopectin and consist of thousand of molecules bonded together with many branches. Unbranched polysaccharides are known as amylase and are one long strand of hundreds of molecules.
Polysaccharides come in two primary forms, structural molecules or storage molecules. Structural Polysaccharides give stability and rigidity to cells. Cellulose is an example of a structural polysaccharide and is used by plants to give structure to the cell walls. Chitin is also another structural polysaccharide and is the substance that is used to create the exoskeleton of some insects and the shells of crustaceans.
Polysaccharides function as the storage unit of energy or glucose for an animal or plant. In humans the storage polysaccharides are called glycogen and in plants they are known as starch. As a molecule of glucose absorbs water it occupies a lot of space in the cell. When glucose is stored as glycogen or starch it does not absorb water and is more tightly packed, which makes it a much more efficient way to store the molecules. Storing glucose in this way allows the body or plant to readily access it when needed and makes sure that the cells do not have too much glucose, which causes raised sugar levels.
The Polysaccharide glycogen is produced by the liver and the muscles in animals. It can also be produced in the brain and stomach. It is stored in the liver and in the muscles. When the body requires quick, instant energy the liver is activated to break down the glycogen into glucose for use in the body. This is done by the release of the hormone glucagon. The glycogen that is stored in muscles is only used by the muscles cells and does not leave the cell. This is to provide quick, instant energy to the muscles in times of need. Glycogen conversion in also triggered by the stress response to allow the fight or flight action need to deal with the situation.