Question

Cellulose is a straight-chain polysaccharide composed of:
A. D-glucose units joined by \[\alpha \] - glycosidic linkages
B. D-glucose units joined by \[\beta \] - glycosidic linkages
C. L-glucose units joined by \[\alpha \]- glycosidic linkages
D. L-glucose units joined by \[\beta \]- glycosidic linkages

Answer 1

Hint: In cellulose the bonds are directed up from the anomeric carbon. Anomeric carbon is defined as the carbon which is derived from the ketone or aldehyde functional group present in the open-chain form of cellulose.

Complete Step by Step Solution:
The chemical formula of cellulose is \[[{({C_6}{H_{10}}{O_5})_n}]\]. Cellulose is the most abundant biopolymer existing on earth. It is a polysaccharide containing thousands of glucose molecules connected together to form a long chain. Cellulose is formed by plants, algae etc. Cellulose is the structural molecule of the plant's cell wall.

Cellulose is a straight-chain polysaccharide composed of \[\beta \] \[(1 \to 4)\] bonds between D-glucose units whereas starch and glycogen are prepared by \[\alpha (1 \to 4)\] glycosidic bonds between the glucose molecule. The linkages present in the cellulose make it a straight-chain polymer.

Cellulose in its pure form is odourless in nature, and hydrophilic. It is insoluble in water. The melting point of cellulose is 467 degrees. Cellulose is degraded to glucose by reacting with acid at high temperatures.

Therefore, Cellulose is a straight-chain polysaccharide composed of D-glucose units joined by \[\beta \] -glycosidic linkages. Thus, option B is correct.

Note: The glycosidic linkage present between the sugar unit 1 and 2 is called \[\beta \] as the bonds are directed up from the carbon derived from the carbonyl functional group (anomeric carbon) whereas the glycosidic linkage present between sugar unit 2 and 3 is called \[\alpha \] as the bond is directed down from the carbon (anomeric carbon).