A glycosidic bond is a covalent linkage formed from the anomeric center of a sugar and another group, commonly an -OH group on a second sugar. Glycosidic bonds connect monosaccharides into disaccharides, oligosaccharides and polysaccharides.

A linkage is described by both the anomeric configuration and the carbon positions it connects. For example, an $\alpha(1\rightarrow4)$ linkage joins carbon 1 of one glucose residue, in the α configuration, to carbon 4 of the next residue.

This notation matters because different linkages produce different three-dimensional structures and biological properties even when the monomer is the same.

Examples built from glucose

Starch and glycogen contain mainly $\alpha(1\rightarrow4)$-linked glucose residues. Branch points are created by $\alpha(1\rightarrow6)$ linkages. Glycogen is typically more highly branched than plant starch.

Cellulose is also a polymer of glucose, but its residues are joined by $\beta(1\rightarrow4)$ linkages. This different stereochemistry favors extended chains that can hydrogen-bond with neighboring chains, producing strong fibrous assemblies.

Thus

same monomer: glucose
        ↓
different glycosidic linkage
        ↓
different polymer geometry and properties

Hydrolysis

Hydrolysis cleaves a glycosidic bond by incorporating water. Enzymes—biological catalysts—can be highly selective for linkage geometry: an enzyme that efficiently cleaves one glycosidic configuration may not cleave another.

This is why humans can digest starch efficiently but cannot digest cellulose using their own digestive enzymes, even though both are glucose polymers.

Carbohydrates are not always simple linear polymers

Short carbohydrate chains can also attach covalently to proteins or lipids, creating glycoproteins and glycolipids. In those contexts, branching and sequence can create molecular recognition patterns rather than serving mainly as energy storage or structural fibers.

Carbohydrate function therefore depends not only on which monosaccharides are present but also on which atoms are connected, the stereochemistry of each glycosidic bond, and the branching architecture of the chain.