Types and Function of Oligosaccharides
Summary
Oligosaccharides are basically carbohydrates formed by the union of three to six units of simple sugars or monosaccharides. However, in rare cases, as many as ten units of sugars have been seen to form an Oligosaccharide. They are either formed by combining molecules of monosaccharides or are formed from the breaking of complex sugars called polysaccharides. Very few oligosaccharides are found in nature from plants. To mention a few; Raffinose is formed of 3 molecules of monosaccharides, melibiose, gentianose and fructose. One oligosaccharide is obtained from arthropod’s blood and in a few plants which are Maltotriose which consists of three molecules of glucose. The molecular formula of Oligosaccharide is C37H62N2O29. It has a calorific va;ue of 1.5-2 cal/gm and is usually found in legumes, garlic, pear, watermelon and white onion. Many fruits also contain fructo-oligosaccharide.- Author Company: BOC Sciences
- Author Name: Linna Green
- Author Email: account@bocsci.com
- Author Website: https://www.bocsci.com/
Types of Oligosaccharides
Disaccharides
These are the sugars having two monomeric units, and thus it is called di_saccharide. Some examples are maltose, sucrose, and lactose. Maltose is the action of an enzyme and it gives glucose +glucose; Sucrose (or cane sugar) in the action of invertase produces fructose + glucose, and Lactose(milk sugar) in the action of enzyme lactase produces galactose + glucose.
Trisaccharides
These contain three monomers like raffinose.
Tetrasaccharides
These contain four monomeric units like stachyose.
Functions
Cell Recognition
All the cells are coated either in glycolipids or glycoproteins, both of which help determine the cell types. Proteins or lectins that bind carbohydrates may recognize the particular oligosaccharides and provide some useful information for cell recognition depending on the oligosaccharide binding.
An important example of oligosaccharide cell recognition is given as the role of glycolipids in blood type determining. Various blood types are distinguished by the modification of glycan that is present on the surface of blood cells. These may be visualized using mass spectrometry. The oligosaccharides that are found on the A, B, and H antigens take place on the non-reducing ends of the oligosaccharide. The H antigen (that indicates an O blood type) serves as a precursor for both the A and B antigens.
Thus, a person with blood type A will have both the A antigen and H antigen present on the glycolipids of the membrane of red blood cell plasma. A person with blood type B will have both the B and H antigens present. And a person with blood type AB will have the three antigens A, B, and H. And finally, a person having blood type O will have only the H antigen. This means that all the blood types contain the H antigen which explains why the blood type O is called the "universal donor."
Cell Adhesion
Several cells produce particular carbohydrate-binding proteins called lectins that mediate cell adhesion with the oligosaccharides. Selectins, which are a family of lectins, mediate certain cell-cell adhesion processes, including those of leukocytes to the endothelial cells. In the immune response, endothelial cells may express certain selectins transiently in response to the injury or damage to the cells.
Also, in response, a reciprocal selectin–oligosaccharide interaction will take place between the two molecules that allow the white blood cell to help to eliminate the damage or infection. Often, Protein-Carbohydrate bonding is mediated by the van der Waals forces and hydrogen bonding.
