This MedLibrary.org supplementary page on Disaccharide is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides.[1]
'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, oligosaccharide, and polysaccharide).
Contents |
Classification
There are two basic types of disaccharides: reducing disaccharides, in which the monosaccharide components are bonded by hydroxyl groups; and non-reducing disaccharides, in which the components bond through their anometric centers.[2]
Formation
It is formed when two sugars are joined together and a molecule of water is removed. For example; milk sugar (lactose) is made from glucose and galactose whereas cane sugar (sucrose) is made from glucose and fructose.
The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond.
Properties
The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties.
Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling.
Common disaccharides
| Disaccharide | Unit 1 | Unit 2 | Bond | Disaccharidase |
| Sucrose (table sugar, cane sugar, saccharose, or beet sugar) | glucose | fructose | α(1→2) | sucrase |
| Lactose (milk sugar) | galactose | glucose | β(1→4) | lactase |
| Maltose | glucose | glucose | α(1→4) | maltase |
| Trehalose | glucose | glucose | α(1→1)α | trehalase |
| Cellobiose | glucose | glucose | β(1→4) | cellobiase |
Maltose and cellobiose are hydrolysis products of the polysaccharides, starch and cellulose, respectively.
Less common disaccharides include:
| Disaccharide | Units | Bond |
| Gentiobiose | two glucose monomers | β(1→6) |
| Isomaltose | two glucose monomers | α(1→6) |
| Kojibiose | two glucose monomers | α(1→2) [3] |
| Laminaribiose | two glucose monomers | β(1→3) |
| Mannobiose | two mannose monomers | either α(1→2), α(1→3), α(1→4), or α(1→6) |
| Melibiose | a glucose monomer and a galactose monomer | α(1→6) |
| Nigerose | two glucose monomers | α(1→3) |
| Rutinose | a rhamnose monomer and a glucose monomer | α(1→6) |
| Xylobiose | two xylopyranose monomers | β(1→4) |
References
- ^ International Union of Pure and Applied Chemistry. "disaccharides". Compendium of Chemical Terminology Internet edition.
- ^ "Disaccharides and Oligiosaccharides". Retrieved on 2008-01-29.
- ^ Matsuda, K. (November 1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature 180: 985. doi:.
External links
|
|||||||||||||||||||||||||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 29 June 2008, at 18:05.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Disaccharide".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.