CLASSIFICATION OF POLYSACCHARIDES:
BASED ON FUNCTION:
1•STORAGE POLYSACCHARIDES: These are polymers of glucose and are reserved energy sources for cell metabolism.They occur as starch in plants, as glycogen in animals and blue green algae and dextran in bacteria and yeast.
(2) GLYCOGEN (Animal Starch):
It is found in liver and muscle cells of all higher animals and human beings. It is a branched polymer of glucose having 5,000-10,000 glucose units. In each glycogen molecule, a-D glucose units are joined by a-1-4 glucosidic linkage. The branches are connected with the main chain by a- 1-6 linkage.
2• STRUCTURE POLYSACCHARIDES: They are also formed by the polymerisation of D-glucose molecules. cellulose and chitin are important structural Polysaccharides.
★AMYLOSE:- It forms 20% of starch and is a straight chain Polysaccharide. The chain is unbranded. ★Each amylose molecule is formed of 300-400 glucose monomers or units. ★It is soluble in hot water. ★its molecular weight ranges from 50,000-60,000. ★It gives blue with iodine. ★Amylose is hydrolysed with bita-amylase enzyme.
★AMYLOPECTIN:- It forms 80% part of starch and is a branched Polysaccharide and it’s chain is coiled. ★ An Amylopectin molecule is formed of thousands of glucose units. ★It is insoluble in water. ★Its molecular weight is more than 5,00,000. ★It gives pink purple colour with iodine. ★Amylopectin is hydrolysed into Dextrins by enzyme beta-amylase.
★STARCH:- It is a storage polysaccharide in plants. ★Amylose chains are unbranched but Amylopectin chains are branched. ★The chains of Amylopectin are branched after every 20-24glucose units. ★Molecular weight of amylose ranges from 50,000-60,000 and of Amylopectin is 5,00,000. ★Insoluble in water.
GLYCOGEN:- It is Animal Starch and is stored in animal cells like liver and muscles. ★Glycogen molecules are branched similar to Amylopectin. ★The glycogen chains are branched after every 8-10 glucose units. ★Molecular weight of each glycogen molecule is 60,00,000 and above. ★Soluble in water.
•CLINICAL SIGNIFICANCE OF GLYCOGEN:-
GLYCOGEN is stored in the muscles and liver cells. Muscle glycogen provides hexose sugars to muscle cells for glycolysis. Liver glycogen provides hexose sugars to all body cells for energy and maintains blood glucose level between meals. Liver glycogen is exhausted after 12-18 hours of fasting,whereas muscle glycogen is exhausted after prolonged vigorous exercise.
Inherited disorders result in glycogen storage diseases. They are caused due to insufficient mobilisation of glycogen and consequently the deposition of glycogen. This causes muscular weakness and may ultimately lead to death.
Sucrose is a condensation product of glucose and fructose. Although glucose and fructose,which make up the structure of sucrose,are reducing sugars, sucrose itself is not a reducing sugar. In sucrose ,the oxygen bridge between the two monosaccharides occurs between carbon 1 of glucose and carbon 2 of fructose, resulting in the elimination of the free carbonyl groups of both these sugars.
★ACTION OF HEAT:- Sucrose melts on heating. Melted sugar on cooling solidifies into pale yellow glassy mass called barely sugar. When heated about 200⁰ C , it loses water to give brown coloured caramel which is used for colouring wines and confectionery.
The starch is the second most abundant carbohydrate found in plants. It occurs in potatoes,rice, wheat,maize,and sago in the form of microscopic granules.