Lacto-N-biose is a disaccharide. It is a key building block of human milk oligosaccharides. Lacto-N-biose is a combination of D-galactose (yellow circle) with N‑acetylglucosamine (GlcNAc) (blue square), connected via a β1‑3 glycosidic bond (Gal β1‑3 GlcNAc) (Fig 412-6). Multiple lacto-N-biose units can be repeated to form HMO-isoforms and other glycans. Another disaccharide important for HMO synthesis (N-acetyllactosamine) is made of the same molecules only with a β1-4 bond (Bode, 2012).