Oligosaccharide

An oligosaccharide (/ˌɒlɪɡoʊˈsækəˌraɪd/; from Ancient Greek (olígos) 'few' and σάκχαρ (sákkhar) 'sugar') is a type of sugar molecule made up of a small number of simple sugars, usually between three and ten linked together. These molecules are important in our bodies and in plants. They can help cells recognize each other and stick together, which is important for many biological processes.

Oligosaccharides are often found attached to other molecules like fats or proteins. When linked to proteins, they are called glycans and can be connected through special bonds. Some oligosaccharides are attached to a specific part of a protein called asparagine, while others attach to threonine or serine. Not all oligosaccharides are part of proteins or fats; some are stored in plants or created when microbes break down bigger sugar molecules like starch or cellulose. These smaller sugar pieces, such as maltodextrins or cellodextrins, play roles in energy storage and transport in nature.

Glycosylation

In biology, glycosylation is the process where a sugar molecule attaches to another organic molecule, helping create important structures like glycoproteins and glycolipids.

N-Linked oligosaccharides connect to a specific part of a protein called asparagine. This happens while the protein is being built, and it may help the protein fold correctly. O-Linked oligosaccharides attach to other parts of proteins, such as threonine or serine, and this process takes place in a cell area called the Golgi apparatus.

Glycosylated biomolecules

Glycoproteins and glycolipids are connected to carbohydrates, and they are very common on the outside of cells. They help keep cells stable and support important cell functions.

Glycoproteins have special oligosaccharide structures that influence their properties, such as how they recognize other cells and how they resist breakdown. Glycolipids help cells recognize each other and send signals. They are made of lipids connected to oligosaccharides and are found in the cell's outer layer, playing a key role in how cells interact and communicate.

Functions

All cells are covered with special molecules called glycoproteins or glycolipids. These help identify what type of cell it is. Proteins called lectins can recognize certain oligosaccharides, which are small chains of sugars, and use this to tell cells apart.

An important example is how blood types are determined. Blood types — like A, B, AB, and O — depend on the oligosaccharides on the surface of red blood cells. The H antigen is present on everyone, but people with A blood have the A antigen too, those with B have the B antigen, those with AB have both A and B, and those with O only have H. This is why O blood is called the "universal donor". Oligosaccharides also help cells stick together, which is important when the body needs to fight infections.

Dietary oligosaccharides

Fructo-oligosaccharides (FOS) are short chains of fructose found in many vegetables. They are a type of soluble dietary fibre and can help with glucose levels in the body. Galacto-oligosaccharides (GOS), made from galactose, are found naturally and are especially important for infants who are not breastfed. Human milk contains oligosaccharides called human milk oligosaccharides (HMOs), which help develop good gut bacteria in infants and can protect against some viruses by acting like decoys.

Mannan oligosaccharides (MOS) are used in animal feed to support gut health. They come from yeast cell walls and work by gathering harmful germs and supporting the immune system.