Polysaccharides are long chains of monosaccharide units linked by glycosidic bonds, typically exceeding 10 residues, forming linear or branched polymers with the general formula (C6H10O5)n where n > 40. These macromolecules assemble via dehydration synthesis, where hydroxyl groups from adjacent monosaccharides form oxygen bridges, yielding structures that range from helical (α-linkages) to fibrous (β-linkages). Heterogeneity arises from slight modifications in repeating units, conferring properties like insolubility or amorphous nature distinct from monosaccharides.
Classification by Composition
Homopolysaccharides contain one monosaccharide type, such as glucose in starch or cellulose, while heteropolysaccharides incorporate multiple types like glucose, galactose, and uronic acids. Linear forms feature straight chains, whereas branched variants, like glycogen, exhibit tree-like architectures for compact storage. This dichotomy influences solubility, digestibility, and enzymatic susceptibility.
Functional Types and Examples
Storage polysaccharides, including starch (amylose and amylopectin in plants) and glycogen (in animals), use α-glycosidic linkages for helical, mobilizable energy reserves. Structural polysaccharides like cellulose (β-linked glucose in plant cell walls) and chitin form rigid fibers via hydrogen bonding between parallel chains. These roles extend to hemicellulose in matrices and galactogen in some invertebrates.
