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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

Formation

Properties

Common disaccharides

References

External links

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.

References

1.

External links

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