Polysaccharides are large carbohydrate molecules composed of long chains of monosaccharide units linked together by glycosidic bonds. They are polymers made up of many sugar molecules, typically more than ten monosaccharides
What molecules do polysaccharides include?
- Monosaccharides: The building blocks of polysaccharides are monosaccharides such as glucose, fructose, galactose, mannose, arabinose, and xylose. The most common monosaccharide in polysaccharides is D-glucose
- Monosaccharide derivatives: Some polysaccharides include amino sugars like D-glucosamine and D-galactosamine, as well as derivatives such as N-acetylneuraminic acid
- Polysaccharides can be homopolysaccharides (homoglycans), composed of only one type of monosaccharide (e.g., starch, glycogen, cellulose-all mainly glucose polymers), or heteropolysaccharides (heteroglycans), composed of different types of monosaccharides
Types and examples of polysaccharides:
- Storage polysaccharides: Starch (plants), glycogen (animals), and galactogen serve as energy storage. Starch consists of amylose (linear α-1,4 linkages) and amylopectin (branched α-1,4 and α-1,6 linkages)
- Structural polysaccharides: Cellulose (plant cell walls) is a linear polymer of glucose with β-1,4 linkages, providing rigidity and insolubility in water. Chitin, found in arthropod exoskeletons and fungal cell walls, is similar to cellulose but includes nitrogen-containing side groups
- Other polysaccharides include hemicellulose, pectins (containing galacturonic acid derivatives), arabinoxylans, and sulfated polysaccharides from algae
Summary
Polysaccharides are complex carbohydrates made from many monosaccharide units (mostly glucose and other sugars) linked by glycosidic bonds. They function primarily in energy storage or as structural components in living organisms. Their molecular structure can be linear or branched, and they may be homopolysaccharides or heteropolysaccharides depending on the monosaccharide composition
