polizaharide

Polizaharide are long, high‑molecular‑weight carbohydrates composed of many monosaccharide units linked by glycosidic bonds. They are among the most abundant natural polymers and serve diverse roles in biology, including energy storage, structural support, and cellular interactions. Their properties depend on the types of monosaccharides, the pattern of linkages, and the degree of branching.

They are broadly classified as homopolysaccharides, which contain a single type of monosaccharide (for example, starch and glycogen, both built from glucose but differing in structure), and heteropolysaccharides, which include several different monosaccharides (such as pectins, xylans, and glycosaminoglycans). Structural polysaccharides, like cellulose in plants and chitin in arthropods and fungi, provide rigidity, while storage polysaccharides, such as starch in plants and glycogen in animals, serve as energy reserves. Other notable categories include mucopolysaccharides and complex extracellular matrix carbohydrates.

Biosynthesis involves enzymes called glycosyltransferases that assemble activated sugar donors into polysaccharide chains. In plants, starch is synthesized in plastids and cellulose at the plasma membrane; in animals, glycogen is produced in liver and muscle tissues. Polizaharide often exhibit variability in length and branching, affecting solubility, viscosity, and digestibility.

Functions extend from structural roles in cell walls and extracellular matrices to energy storage and regulation of cell signaling and recognition. Dietary polysaccharides range from digestible starch and glycogen to non-digestible fibers like cellulose, which are fermented by gut microbiota. Industrial and medical applications include thickeners, gelling agents, biomaterials, and drug delivery systems. Common examples encompass starch, glycogen, cellulose, chitin, pectin, alginate, and inulin.