Disaccharide
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.
ReferencesISBN links support NWE through referral fees
- ↑ International Union of Pure and Applied Chemistry. "disaccharides". Compendium of Chemical Terminology Internet edition.
External links
- MeSH Disaccharides
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