noun, plural: monosaccharides
Carbohydrates are organic compounds comprised of carbon, hydrogen, and oxygen, usually in the ratio of 1:2:1. They are one of the major classes of biomolecules. They are an important source of energy. They also serve as structural components. They are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. The most fundamental type is the simple sugars called monosaccharides. An oligosaccharide is a carbohydrate that is relatively smaller than a polysaccharide. The component monosaccharide units of an oligosaccharide are not rigorously defined. There are references that consider carbohydrates comprised of two to ten monosaccharide units as oligosaccharide, thus, including disaccharides (which are saccharides made up of two monosaccharide units). There are other references that classify carbohydrates consisting of three to six monosaccharide constituents as oligosaccharides.
The oligosaccharide is comprised of monosaccharide units joined by glycosidic bonds. Many of the naturally-occurring oligosaccharides are linked to another biomolecule, such as proteins, peptides, and lipids. Carbohydrates that are covalently linked to another biomolecule via glycosylation are referred to as glycoconjugates and the carbohydrate constituent of the complex is called a glycan. For instance, a glycolipid is a carbohydrate (e.g. certain oligosaccharides and polysaccharides) attached to a lipid. A glycoprotein is a carbohydrate attached to a protein.
Examples of oligosaccharides are raffinose, maltotiriose, maltotetralose, maltopentalose, laltotriose, melibiose, etc. Many of them serve as the glycan component of a glycoconjugate and as such are associated with various biological functions, such as cell recognition, cell binding, immune response, etc.
Word origin: from Greek olígoi (“few”): single + sacchar ("sugar")