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Classification of Carbohydrates and it's function

Carbohydrate :

Carbohydrates are defined as polyhydroxy aldehydes or ketones and their derivatives or substances which yield one of these substance on hydrolysis.


Classification of carbohydrate :

Carbohydrate are known as saccharides which come from the Greek word sachron. Which means sugar.
Carbohydrate,classification of carbohydrate,definition of carbohydrate, biochemistry notes
Carbohydrate Classification

It is mainly of 3 types-

1. Monosaccharides
2. Oligosaccharides
3. Polysaccharides
Monosaccharide and oligosaccharide are sweet in taste, crystalline in nature and soluble in water.


1. Monosaccharide :

These are the simplest group of carbohydrates and are called simple sugar. They have general formula Cn(H2O)n If the value of n =6 then it becomes C6H12O6 Which is glucose.
-  They can not be further hydrolysed.
-  Based on the functional group they are classified as Aldose and ketose.
Difference between Aldose and ketose.


Aldose :

Here the functional group is aldehyde ( -CHO) e.g. Glucose is Glyseraldehyde.


Ketose :

Here the functional group is ketone( C=O) eg. Fructose is dihydroxy acetone.


Based on the carbon atoms monosaccharides are regarded as :

Triose (3C)
Tetrose (4C)
Pentose (5C)
Hexose (6C)
Heptose (7C)
Hence glucose is Aldohexcose.


2. Oligosaccharide :

Oligosaccharide contains two to ten molecules of monosaccharide unit which are liberated on hydrolysis.
Based on monosachharide unit present. It is further sub divided in to -
1. Disaccharides
2. Trisaccharides
3. Tetrasaccharides
4. Pentasaccharides


1. Disaccharides :

- The general formula of disaccharide is Cn(H2O)n 
- Disaccharide on hydrolysis produce two molecules of same or different monosaccharide.
Eg.  Maltose  ---------->  Glucose + Glucose
        Sucrose  -------->  Glucose + Fructose
        Lactose  ------->  Glucose + Galactose


2. Trisaccharide :

Trisaccharide on hydrolysis produce three molecules of same or different monosaccharide.
Eg. 
Raffinose----------> Glucose+Fructose+ Galactose


3. Tetrasaccharide :

Tetrasaccharides on hydrolysis to produce four molecules of same or different monosaccharides.
Eg. 
Stachyose ---------> Glucose+Fructose+2Galactose


4. Pentasaccharide :

Pentasaccharides on hydrolysis produce five molecules of same or different monosaccharides.
Eg. 
Verbascose  ---------> Glucose+Fructose+3Galactose


3. polysaccharide :

These are polymers of monosaccharide with high molecular weight. They usually tasteless and form colloids with water. It is of two types .
1. Homo polysaccharide
2. Hetero polysaccharide


Homo polysaccharide :

They contain monosaccharide of single type. E.g. Starch, glycogen, cellulose, insulin agar and dextrans.


Hetero polysaccharide :

They contain two or more monosaccharides. E.g. Heparin, chondroitin sulphate , pectin and mucopolysaccharides.


Function of carbohydrates :

-  They are the most abundant dietry source of energy for all organism.
-  They form constituents of compound lipids and conjugated proteins.
-  Carbohydrates are structural component for many organism.
-  Carbohydrates also serve as a storage form of energy.
-  Certain carbohydrate derivatives are used as drug like cardiac glycosides and antibiotics.
-  Some products of carbohydrate metabolism act as catalysts or promotors.
-  Carbohydrates provide raw materials for a number of industries like textile, artificial silk, paper and fermentation etc.


Qualitative test for carbohydrates :


1. Molischs test :

1 ml of the aqueous suspension of the sugar is taken in a test tube. To this 2 drops of an alcoholic solution of alpha naphthol is added and shaken well. Then 2 ml of con. H2SO4 is added carefully by the side of the test tube. A reddish violet ring at the junction of the two layers indicate the presence of carbohydrate.


2. Fehlings test :

1 ml of the test solution and 2ml of Fehling solution are boiled in a test tube for 2 minutes. A brick red precipitate indicate the presence of carbohydrate.


3. Benedict's test :

1 ml of an aqueous solution of the test substance and 2 ml of Benedict's reagent are boiled in a test tube for 2 minutes. A brick red precipitate indicate the presence of carbohydrate.


4. Iodine test :

2 ml of the test solution is treated with 1 ml of iodine solution. A blue precipitate indicates the presence of starch.


Carbohydrates definition, classification, structure and its function. What are carbohydrates sources, carbohydrates rich food.









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