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Carbohydrates are the organic compounds i.e. essential biomolecules composed of carbon ,hydrogen and oxygen. The hydrogen and oxygen are in the ratio of 2:1 so they are also called "Hydrates of Carbon". They are also called Saccharides (Latin: Saccharon:Sugar)

They are represented by the general formula Cn(H2O)n. They are aldehyde and ketone derivatives of polyhydroxy alcohol.

1) Polyhydroxy aldoses: having aldehyde (-CHO) group. Eg: Glucose

2) Polyhydroxy ketoses: having (-CO) group .Eg: Fructose

According to the complexity of chemical substances of which they are formed ,carbohydrates are grouped into following types.

  1) Monosaccharides.  

  2) Oligosaccharides 

  3) Polysaccharides 

Monosaccharides   :

.Simplest form of carbohydrates composed of 3-7 carbon atoms which cannot be further hydrolyzed.     

.Water soluble, low molecular weight, reducing sugar and sweet in taste.   

.Their general formula is Cn(H20)n

.Glucose or aldohexose (C6 H12O6) is the most common monosaccharide found in nature. It contains five hydroxy groups and one aldehyde group. It is white, crystalline, sweet tasting substance highly soluble in water.


Oligosaccharides are composed of 2-10 molecules of monosaccharides. These monosaccharides are linked by glyosidic linkage. Glyosidic linkage refers to a covalent bond formed by condensation of two monosaccharides with release of one molecule of water. 

The most common oligosaccharide is disaccharide whose general formula is Cn (H2O) n-1. They are soluble in water and sweet in taste. The common examples of disaccharides are sucrose, maltose, lactose etc.

Sucrose: Glucose+ Fructose (Source: Sugarcane, Sugar beets)

Lactose: Glucose+ Galactose (Source: Milk)

Maltose: Glucose+ Glucose (Intermediate product of starch)


They are complex carbohydrates formed by condensation of many monosaccharides linked by glyosidic bond. They have high molecular weight. They are insoluble in water and not sweet in taste. They yield monosaccharides on hydrolysis.  They are of two types:  1)Homopolysaccharides 

2) Heteropolysaccharides 

Homopolysaccharides  are formed by condensation of one type of monosaccharides. Eg: Starch, Glycogen, Cellulose , Chitin etc.

Heteropolysaccharides are made of two or more type of monosaccharides. Eg: Agar, Peptidoglycan, mucilage etc.