Question

The correct statement about the following disaccharide is :

(A) Ring (a) is pyranose with $\alpha$- glycosidic link
(B) Ring (a) is furanose with $\alpha$- glycosidic link
(C) Ring (b) is furanose with $\alpha$- glycosidic link
(D) Ring (b) is pyranose with $\beta$- glycosidic link

Answer 1

A disaccharide is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are soluble in water. A glycosidic linkage or bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate.

Complete step by step answer:
1,4 glycosidic bonds are formed due to condensation reactions between a hydroxyl oxygen atom on carbon-4 on one sugar and the $\alpha$-anomeric form of C-1 on the other.There are two types of glycosidic bond- 1,4 $\alpha$ glycosidic bonds and 1,4 beta glycosidic bonds.
1,4 $\alpha$ glycosidic bonds are formed when the OH on the carbon-1 is below the glucose ring ; while 1,4 beta glycosidic bonds are formed when the OH is above the plane.
The ring (i) is pyranose with $\alpha$ glycosidic linkage. The six membered cyclic structure of glucose is called pyranose structure, in analogy with pyran which is a cyclic organic compound with one oxygen and five carbon atoms in the ring. The ring (i) is pyranose with $\alpha$ glycosidic linkage which means the oxide linkage which connects the monosaccharide units in polysaccharide below the plane.
So, the correct answer is “Option A”.

Note: A glycosidic linkage is formed between the hemiacetal or hemiketal group of a saccharide and the hydroxyl group of some compound such as an alcohol. The five membered cyclic structure of carbohydrates is called pyranose structure.