Illustration of the linkage points for oligomer formation in biomolecules by arrows. The phosphodiester bond in nucleic acid biosynthesis (a) and the peptide bond in protein biosynthesis (b) yield linear oligomers. In contrast, the glycosidic linkage in oligosaccharides can involve any hydroxyl group, opening the way to linear and also branched structures (c). Using d-glucose (Glc) as an example, its active form UDP-Glc allows conjugation of this sugar to carbohydrate acceptors to any hydroxyl group, as symbolized by arrows directed towards the hydroxy groups (for list of resulting diglucosides, please see Table 1). The anomeric position in chain elongation can vary, as symbolized by two bold arrows pointing away from the molecule (from , with permission).