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Sucrose, a common 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 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

DisaccharideUnit 1Unit 2BondDisaccharidase
Sucrose (table sugar, cane sugar, saccharose, or beet sugar)glucosefructoseα(1→2)sucrase
Lactose (milk sugar)galactoseglucoseβ(1→4)lactase
Maltoseglucoseglucoseα(1→4)maltase
Trehaloseglucoseglucoseα(1→1)αtrehalase
Cellobioseglucoseglucoseβ(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]; 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

1. ^ International Union of Pure and Applied Chemistry. "disaccharides". Compendium of Chemical Terminology Internet edition.
2. ^ Matsuda, K. (November 1957). "Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis". Nature 180: 985. DOI:10.1038/180985a0. 

External links

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Major families of biochemicals
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Analogues of nucleic acids:Types of CarbohydratesAnalogues of nucleic acids:
General: Aldose | Ketose | Pyranose | Furanose
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Hexoses: Glucose | Galactose | Mannose | Gulose | Idose | Talose | Allose | Altrose | Fructose | Sorbose | Tagatose | Psicose | Fucose | Rhamnose
Disaccharides: Sucrose | Lactose | Trehalose | Maltose
Polymers: Glycogen | Starch (Amylose | Amylopectin) | Cellulose | Chitin | Stachyose | Inulin | Dextrin
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Sugars, brown
Nutritional value per 100 g (3.5 oz)
Energy 0 kcal   0 kJ

Carbohydrates     97.33 g
- Sugars  96.21 g
- Dietary fiber  0 g  
Fat 0 g
Protein 0 g
Water 1.77 g
Thiamin (Vit. B1)  0.
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Monosaccharides (from Greek : single, sacchar: sugar) are the simplest carbohydrates. They cannot be hydrolyzed into simpler sugars. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste.
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Monosaccharides (from Greek : single, sacchar: sugar) are the simplest carbohydrates. They cannot be hydrolyzed into simpler sugars. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste.
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An oligosaccharide is a saccharide polymer containing a small number (typically three to ten[1]) of component sugars, also known as simple sugars.

They are generally found either O- or N
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Polysaccharides are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic bonds. They are therefore very large, often branched, macromolecules. They tend to be amorphous, insoluble in water, and have no sweet taste.
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Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage. Lactose makes up around 2-8% of the solids in milk. The name comes from the Latin word for milk, plus the -ose ending used to name sugars.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Galactose (Gal) (also called brain sugar[1]) is a type of sugar which is less sweet than glucose and not very water-soluble. It is considered a nutritive sweetener because it has food energy.

Galactan is a polymer of the sugar galactose.
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Sucrose (common name: table sugar, also called saccharose) is a disaccharide (glucose + fructose) with the molecular formula C12H22O11. Its systematic name is α-D-glucopyranosyl-(1→2)-β-D-fructofuranose.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods and is one of the three most important blood sugars along with glucose and galactose. Honey, tree fruits, berries, melons, and some root vegetables, such as beets, sweet potatoes, parsnips, and
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Monosaccharides (from Greek : single, sacchar: sugar) are the simplest carbohydrates. They cannot be hydrolyzed into simpler sugars. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste.
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dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions.
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A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule.[1]
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In chemistry, a glycosidic bond is a certain type of functional group that joins a carbohydrate (sugar) molecule to an alcohol, which may be another carbohydrate. Specifically, a glycosidic bond is formed between the hemiacetal group of a saccharide (or a molecule derived from a
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Sugars, brown
Nutritional value per 100 g (3.5 oz)
Energy 0 kcal   0 kJ

Carbohydrates     97.33 g
- Sugars  96.21 g
- Dietary fiber  0 g  
Fat 0 g
Protein 0 g
Water 1.77 g
Thiamin (Vit. B1)  0.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomers (mirror images of each other). Diastereomers can have different physical properties and different reactivity.
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Monosaccharides (from Greek : single, sacchar: sugar) are the simplest carbohydrates. They cannot be hydrolyzed into simpler sugars. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste.
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Disaccharidase is a type of enzyme that breaks down disaccharides into monosaccharides.

Examples of disaccharidases

  • Lactase (breaks down lactose into glucose and galactose)
  • Maltase (breaks down maltose into 2 glucoses)

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Sucrose (common name: table sugar, also called saccharose) is a disaccharide (glucose + fructose) with the molecular formula C12H22O11. Its systematic name is α-D-glucopyranosyl-(1→2)-β-D-fructofuranose.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods and is one of the three most important blood sugars along with glucose and galactose. Honey, tree fruits, berries, melons, and some root vegetables, such as beets, sweet potatoes, parsnips, and
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Sucrase is the name given to a number of enzymes that catalyse the hydrolysis of sucrose to fructose and glucose.

Types

  • EC 3.2.1.10 is sucrase-isomaltase
  • EC 3.2.1.26 is invertase
  • EC 3.2.1.

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Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage. Lactose makes up around 2-8% of the solids in milk. The name comes from the Latin word for milk, plus the -ose ending used to name sugars.
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Galactose (Gal) (also called brain sugar[1]) is a type of sugar which is less sweet than glucose and not very water-soluble. It is considered a nutritive sweetener because it has food energy.

Galactan is a polymer of the sugar galactose.
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Lactase (LCT), a member of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers.
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Maltose, or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) linkage. It is the second member of an important biochemical series of glucose chains.
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Maltase (EC 3.2.1.20 ) is an enzyme produced by the cells lining the small intestine which specifically breaks down the disaccharide maltose. It comes under the enzyme category carbohydrase (which is a subcategory of hydrolase), and the disaccharide it hydrolyses is maltose.
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