Carbohydrates :
They are commonly called as “‘sugar’’. They are maximum among the organic biomolecules found on the earth. They are the organic compounds of carbon (C), hydrogen (H) and oxygon (O) in 1:2:1 ratio. Their general formula is (CH2O)n. They have two or more hydroxyl groups and one aldehyde (-CHO) or ketone (-CO) group. Most of the carbohydrates are the constituent of food and are the main source of energy. On the basis of chemical composition, they are of three types-
(A) Monosaccharides
They are simplest carbohydrates which are soluble in water and sweet in taste. They consists of 3 to 7 carbon atoms. Glucose, Fructose and Galactose are the 6 carbon containing monosaccharides. Their chemical formula is C6H12O6 and they are isomers. Glucose and fructose are the maximum occurring sugars in the nature. Glucose is also called as dextrose and it is used mainly in the formation of energy. Five carbon containing ribose is another important monosaccharide which participate in the synthesis of DNA and RNA.
Fructose (Fruit sugar) is tire sweetest natural occurring sugar. Tire artificially synthesized Saccharin is about 200-times more sweeter than fructose.
(B) Disaccharides
They are soluble in water and sweet in taste. They consist of two monosaccharides linked by a glycosidic bond. It forms one molecule of water.
Sucrose (cane sugar), Maltose (fruit sugar) and Lactose (milk sugar) are the examples of disaccharides. Maltose is found in the sprouted grains, sucrose in the sugar can and lactose is found in the milk.
The carbohydrates formed by the condensation of three to ten monosaccharides are called as oligosaccharides.
(C) Polysaccharides
They are insoluble in water and tasteless. They are formed by polymerization of monosaccharide units and their general formula is (C6H10O5)n. Starch in plants and Glycogen in animals are two common polysaccharides & they are formed by the polymerization of glucose. Insulin and some others are formed by the polymerization of fructose. Glycogen is also called as Animal Starch
The polysaccharides are normally the stored food material in the animals and plants because they hydrolyses easily to form monosaccharides.
Cellulose and Chitin are also polysaccharides. The cellulose is used in the formation of cell wall in the plants and the chitin is used in the formation of exoskeleton of insects and other arthropods. Significance of Carbohydrates
- They are the primary source of energy.
- They are used in the formation of cell wall and connective tissues.
- Starch in plants and glycogen in animals are the stored form of food.
- Chitin is used in the formation of exoskeleton of insects & other arthropods.
- Ribose is used in the formation of RNA and DNA.
