Disaccharide: Difference between revisions
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</ref>; [[Nigerose]], that consists of two [[glucose]] [[monomer]]s with an α(1→3) linkage; and [[Xylobiose]], that consists of |
</ref>; [[Nigerose]], that consists of two [[glucose]] [[monomer]]s with an α(1→3) linkage; and [[Xylobiose]], that consists of two [[xylopyranose]] [[monomer]]s with a β(1→4) linkage. |
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== References == |
== References == |
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Revision as of 01:17, 10 September 2007
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).
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) that leads to the loss of a molecule of water.
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.
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: Gentiobiose, that consists of two glucose monomers with an β(1→6) linkage; Isomaltose, that consists of two glucose monomers with an α(1→6) linkage; Kojibiose, that consists of two glucose monomers with an α(1→2) linkage [2]; Nigerose, that consists of two glucose monomers with an α(1→3) linkage; and Xylobiose, that consists of two xylopyranose monomers with a β(1→4) linkage.
References
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "disaccharides". doi:10.1351/goldbook.D01776
- ^ Matsuda, K. (1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature. 180: 985. doi:10.1038/180985a0.
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External links
- Disaccharides at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
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