Carbohydrates

Carbohydrates:

Introduction of carbohydrates
Carbohydrates are the organic molecules that are composed of elements carbon, hydrogen and oxygen.

Classification of carbohydrate

Carbohydrates are classified into three groups based on the number of sugar units and upon their behaviour towards hydrolysis. They are
>Monosaccharides
>Oligosaccharides and
>Polysaccharides

Monosaccharides:

These are simplest group of carbohydrates and are referred as simple sugars as they are sweet in taste. 
They cannot be further hydrolyzed to simpler compounds.
They have the general formula C_n(H₂O)_n

Examples: Glucose and fructose

Oligosaccharides:

These carbohydrates liberate two to ten monosaccharide molecules on hydrolysis.

 They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc. based on the number of monosaccharide units. 

For e.g., disaccharides like sucrose produce two molecules of monosaccharides on hydrolysis. 

Polysaccharides:

These carbohydrates liberate a large number of monosaccharide molecules on hydrolysis. They are usually amorphous, insoluble in water and tasteless and are called non-sugars. 

They are again sub-divided into two types. They are homopolysaccharides and heteropolysaccharides

Open and ring structure of Sucrose:

Sucrose is made up of a-D-Glucose and b-D-fructose held together by a glycosidic bond, between C₁ of a-glucose and C₂ of b-fructose. The reducing groups of glucose and fructose are involved in glycosidic bond, so it is a non-reducing sugar.

Ring structures:

Maltose:

Maltose is made up of two a-D-glucose (in pyranose form) units held together by a(1-->4) glycosidic bond. As there is a free aldehyde group at C-1 position of the second glucose molecule, maltose is known as reducing sugar. Maltose forms osazones. The enzyme that hydrolyses maltose is maltase.

lactose:

Lactose is made up of b-D-galactose and b-D-glucose held together by b(1-->4) glycosidic bond. As the aldehyde group at C-1 position of glucose is free, lactose is known as reducing sugar. Lactose forms osazones.

Partial representation  of structure  of  starch:

Starch is a white amorphous powder, insoluble in cold water. 

It solution in water gives a blue color with iodine solution. 

The blue color disappears on heating and reappears on cooling. 

Partial Representation of structure of 

cellulose:

It is a colourless amorphous solid which decomposes on heating. 

It is largely linear and its individual strands align with each other through multiple hydrogen bonds.

Glycogen:

The structure of glycogen consists of long polymer chains of glucose units connected by an alpha acetal linkage. 

The graphic on the left shows a very small portion of a glycogen chain. 

All of the monomer units are alpha-D-glucose, and all the alpha acetal links connect C # 1 of one glucose to C # 4 of the next glucose.

Carbohydrates are source of energy /functions:

1)Carbohydrates are most abundant dietary source of energy for all organisms.

2)They supply energy and serve as storage form of energy.

3)Carbohydrates such as glucose, fructose, starch, glycogen, etc. provide energy for functioning of living organisms.

4)Carbohydrates are utilizes as raw materials for several industries. For e.g., paper, plastics, textiles etc.

5)Polysaccharides like cellulose act as chief structural material for cell walls in plants.

6)Carbohydrates participate in cellular functions such as cell growth, adhesion and fertilization