Oligosaccharides



Properties and  Role of  Oligosaccharides:

This group consists of derivatives of monosaccharides.
Those carbohydrates which upon hydrolysis yield 2 to 10 saccharide units are called oligosaccharides. On the basis of number of saccharide units, the oligosaccharides are classified :

1. Disaccharides
2. Trisaccharides
3. Tetrasaccharides

The most common among these are disaccharides.



1. Disaccharides

Two monosaccharides combine to form a disaccharide. It is a kind of oligosaccharides. Disaccharides are less sweet in taste and less soluble in water. These can be hydrolyzed to give monosaccharides. Examples are: maltose, lactose, sucrose. The general formula of disaccharide is: C12 H22 011. Some common disaccharides are as follows: 

Sucrose: It is commonly known as cane sugar. It is widely used as sweetener at homes for making sweet dishes. In plants sucrose is also called transport disaccharide as prepared food in plants is transported in the form of sucrose. It is very soluble and can therefore be moved efficiently in high concentration in plants. It is also relatively unreactive chemically. The sucrose is formed by the condensation of glucose and fructose. In this reaction, the -OH group at C-1 of glucose reacts with the OH group at C-2 of fructose, liberating a water molecule forming a-1,2-glycosidic linkage.

Formation of sucrose



Maltose: It is commonly known as malt sugar. It is an intermediate disaccharide produced during the breakdown of starch and glycogen. Maltose is generally found in germinating seeds. The maltose is formed by the condensation of two a-glucoses. In this reaction, the -OH group at C-1 of one glucose reacts with the -OH group at C-4 of other glucose, liberating a water molecule forming a-1, 4-glycosidic linkage.

Formation of Maltose



Lactose: It is commonly known as milk sugar. The lactose is formed by the condensation of B- galactose and B-glucose. In this reaction, the -OH group at C-1 of galactose reacts with the -OH group at C-4 of glucose, liberating a water molecule forming B-1, 4-glycosidic linkage.

Formation of Lactose







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