AskDefine | Define disaccharide

Dictionary Definition

disaccharide n : any of a variety of carbohydrates that yield two monosaccharide molecules on complete hydrolysis

User Contributed Dictionary

English

Noun

  1. Any sugar, such as sucrose, maltose and lactose, consisting of two monosaccharides combined together.

Translations

a sugar consisting of two monosaccharides
  • French: disaccharide
  • Italian: disaccaride
  • Swedish: disackarid

Extensive Definition

A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides.
'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, oligosaccharide, and polysaccharide).

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.

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

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 ; Laminaribiose, that consists of two glucose monomers with a β(1→3) linkage; Mannobiose, that consists of two mannose monomers with either an α(1→2), α(1→3), α(1→4), or an α(1→6) linkage; Melibiose, that consists of a glucose monomer and a galactose monomer with an α(1→6) linkage; Nigerose, that consists of two glucose monomers with an α(1→3) linkage; Rutinose, that consists of a rhamnose monomer and a glucose monomer with an α(1→6) linkage; and Xylobiose, that consists of two xylopyranose monomers with a β(1→4) linkage.

References

External links

disaccharide in Arabic: سكر ثنائي
disaccharide in Bosnian: Disaharidi
disaccharide in Bulgarian: Дизахарид
disaccharide in Czech: Disacharidy
disaccharide in German: Zweifachzucker
disaccharide in Estonian: Disahhariidid
disaccharide in Spanish: Disacárido
disaccharide in Esperanto: Disakarido
disaccharide in Basque: Disakarido
disaccharide in French: Diholoside
disaccharide in Galician: Disacárido
disaccharide in Icelandic: Tvísykrur
disaccharide in Italian: Disaccaridi
disaccharide in Hebrew: דו-סוכר
disaccharide in Latin: Disaccharides
disaccharide in Lithuanian: Disacharidas
disaccharide in Macedonian: Дисахарид
disaccharide in Malay (macrolanguage): Disakarida
disaccharide in Dutch: Disacharide
disaccharide in Japanese: 二糖
disaccharide in Norwegian: Disakkarid
disaccharide in Occitan (post 1500): Disacarid
disaccharide in Polish: Disacharydy
disaccharide in Portuguese: Dissacarídeo
disaccharide in Russian: Дисахариды
disaccharide in Albanian: Disakaridet
disaccharide in Simple English: Disaccharide
disaccharide in Finnish: Disakkaridi
disaccharide in Swedish: Disackarider
disaccharide in Thai: ไดแซ็กคาไรด์
disaccharide in Ukrainian: Дисахариди
disaccharide in Chinese: 雙醣
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