Glycan complexes appear from the assembly of units of different sugars called monosaccharides. These sugars are organic compounds that contain at least one unsaturation (aldehyde, ketone, cycle) as well as a poly-hydroxylated carbon chain. This chain is typically composed of 5 (pentoses) or 6 (hexoses) carbon atoms. Since these atoms are most often asymmetric, all monosaccharides contain a high density of stereochemical information.
Sucrose (table sugar) is a disaccharide which comes from the condensation of a molecule of glucose and a molecule of fructose. However, the glycans present in living organisms are of great diversity and much greater complexity. The chemical structures of the ten most abundant monosaccharides in mammalian glycans are described below. Some sugars differ only in their stereochemistry (mannose is an epimer of glucose) while other monosaccharides show more pronounced chemical differences (NeuAc vs. Glc). In an effort to represent glycan complexes, the glycoscience community has agreed on a nomenclature and a symbolic representation that uses several shapes and colors.