Carbohydrates I Classification, Sources and Functions (Simple & Easy Note)

Carbohydrates I Classification, Sources and Functions

These are organic compounds, composed of carbon, hydrogen, and oxygen. Their amount is about 1% in the protoplasm. They occur in all living organisms.

CLASSIFICATION OF CARBOHYDRATES

According to the size of the molecule the carbohydrates are classified into three groups;
1) Mono-saccharides                  2) Di-saccharides                          3)  Poly-saccharides

      

      1)    Mono-saccharides:
These are the carbohydrates which cannot be further changed into simple sugar. E.g. Glucose and Fructose.

         

According to the number of carbon atoms, the carbohydrates are of different kinds.

                                 i.            Trioses: These sugars contain 3-carbon atoms.

                               ii.            Tetroses: These sugars contain 4-carbon atoms.

                             iii.            Pentoses: These sugars have 5-carbon atoms.

                             iv.            Hexoses: These sugars have 6-carbon atoms.

All the monosaccharides are found in white solid crystals. They have a sweet taste and easily soluble in water.

Sources:
The mono-saccharides are mostly found in vegetables. Glucose and Fructose are present in grapes. Fructose is the sweetest sugar, it is also found in honey. In milk lactose sugar is present and galactose is a part of it. The glucose, fructose, and galactose are the hexose sugars.

       2)    Oligosaccharides and Disaccharides:
These carbohydrates are composed of two to ten monosaccharide compounds. On Hydrolysis, these oligo-saccharides produce two to ten monosaccharide molecules.

The carbohydrates that are formed by the union of two sugars are called disaccharides.

These carbohydrates are formed by the union of two similar or different sugars. This chemical process is called condensation, in which a water molecule is liberated. The examples of disaccharides are as follows:

                                 i.                Glucose + Glucose --------------------→    Maltose + Water.

                               ii.            Glucose + Fructose -------------------→     Sucrose + Water.

                             iii.            Glucose + Galactose ------------------→      Lactose + Water.

Sources:
Sucrose is a common sugar that is widely used. It is obtained from sugarcane or beet. It is formed by the combination of glucose and fructose. Sugarcane and beet are cultivated for the production of sucrose.

    

       3)    Poly-saccharides:

Polysaccharides are the carbohydrates which are formed by the combination of many mono-saccharides, e.g Starch, Glycogen, Cellulose, etc.

Starch:

It is composed of many glucose molecules which are linked together in straight or branched manner.

The starch is present in the leaves, roots, and seeds in granular form, for example, wheat, potato, rice, etc. It is insoluble in water, but when boiled it becomes soluble. By hydrolysis, it is broken into sugars and takes part in the production of energy by oxidation.

                  24C₆H₁₂O₆  ------------------→ C₁₄₄H₂₄₀O₁₂₀   + 24H₂O

                     Glucose                                                        Potato Starch

Glycogen:

It is animal starch. When many glucose molecules are linked together in a chain-like manner, glycogen is formed. It occurs in the muscles and liver of animals. It is also found in bacteria and fungi.

                The glycogen is prepared by the liver which converts the extra glucose into glycogen. This glycogen is stored in the liver and muscles. When there is a shortage of glucose in the body, then glycogen is again converted into glucose to provide energy. In this way, the amount of glucose remains in balance in the blood of the body.

The glycogen is insoluble in water.

Cellulose:

It is composed of many molecules of glucose from about 2000 to 3000. It is only formed in the body of plants and occurs in the cell wall.

                In the body of animals, the cellulose cannot be digested by enzymes. In their digestion, some special types of bacteria are involved which are present in the caecum of the alimentary canal. These bacteria digest the cellulose by the action of certain enzymes.

FUNCTIONS:

1.     Carbohydrates produce energy by oxidation, which is used in various functions.

2.     Carbohydrates may be changed into other substances. The extra amount of glucose in plants is converted into starch, which can be changed again into glucose at the time of requirement. In animals they are changed into glycogen.

3.     The complex carbohydrate molecules form the body of living organisms. They also make the organs strong. Cellulose is also formed from carbohydrates in plants.