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Today our topic is Disaccharide and Glycosidic linkage.
Speaker Sonali Ghatak & Editor Anindya Bhattacharya.
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So, let’s start
Disaccharide.
A disaccharide
A disaccharide consists of two sugars joined by an O-glycosidic bond.
In the disaccharide, two monosaccharides are
joined by acetal or glycoside formation.
The hemiacetal –OH of one 
monosaccharide and an –OH of second monosaccharide,
dehydrate to form glycosidic bond.
A  bond forms between anomeric or first (Carbon1) carbon  and the alkoxy oxygen.
Glycosidic linkages are named by reading from left to right.
Example-
1. In
Sucrose anomeric carbon atoms of a glucose
unit and a fructose unit are
joined through alpha1-2beta glycosidic linkage.
Alpha for glucose beta for fructose
 
2. The disaccharide maltose contains two D-Glucosejoined by C-1 of one glucose C-4 of another glucose.
The configuration of the two D-glucose residue is alpha
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3. Lactose, the disaccharide of milk,consists of galactose joined to glucose by beta 1,4-glycosidic
linkage. Here , occurrence and biochemical roles of
some disaccharides.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sucrose- Glucose+Fructose- a product of photosynthesis
Lactose- ( Galactose+Glucose)- energy source
Trehalose-( Glucose+Glucose)-circulatory sugar
in insects, used for energy
Maltose-( Glucose+ Glucose)- the dimer derived
from the starch and glycogen
Cellobiose-( Glucose+Glucose)- dimer of the
cellulose polymer
Gentiobiose- (glucose+ glucose) - constituents
of plant glycosides
and 
some polysaccharides.
The disaccharides are 
of two types:
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, trehalose.
So, we completed Disaccharide. In 
next video we will discuss about Hydrolysis of Sucrose.
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