DISACCHARIDES - EASY NOTES

Made of two molecules of monosaccharides

The two monosaccharides are joined together by O – glycosidic linkage.

The O- glycosidic linkage is formed when –OH group of monosaccharide reacts with anomeric carbon of other.

Sub classified on the basis of the presence or absence of free reducing (aldehyde or ketone) group

1.Reducing disaccharides with free aldehyde or keto group, e.g. maltose, lactose

2.Non-reducing disaccharides with no free aldehyde or keto group, e.g. sucrose.

 1. Maltose - Reducing Disaccharide

--Made of two glucose units joined together by α 1, 4 -glycosidic linkage formed between the anomeric carbon of one glucose unit and fourth carbon of other glucose unit.

--the first carbon of one glucose unit is free and so maltose is a reducing disaccharide

--Maltose is produced from starch by amylase.

Isomaltose:

--Made of two glucose units joined together by α 1,6 glycosidic linkage

--By product formed during digestion of starch along with glucose and maltose.

2. Lactose- Reducing Disaccharide

--Also called as Milk sugar

--Made of galactose and glucose joined by β 1, 4 linkage.

--Reducing in nature.

--The first carbon of the glucose unit is available for oxidation and thus lactose is a reducing disaccharide.

--Lactose is hydrolysed to glucose and galactose by lactase enzyme in human beings

Sucrose – Non - Reducing Disaccharides

--Also called as Common table sugar

--Made of glucose and fructose joined by α 1 ->2 β linkage.

--Since both anomeric carbons (1st carbon in glucose and 2^nd carbon in fructose) are involved in linkage and no anomeric carbon left for oxidation, sucrose is non-reducing in nature.