The disaccharide that is constituted of two glucose units is

Options

A. sucrose
B. lactose
C. maltose
D. cellobiose

Answer

D

Explanation

Disaccharide, maltose is composed of two `alpha-D-` glucose units in which `C1` is of one glucose is linked to `C4` of another glucose unit. In solution, the free aldehyde group can be produced at `C1` of second glucose in solution, hence maltose shows reducing properties.
Partial hydrolysis of cellulose (cotton fibres) gives the disaccharise cellobiose, `C_(12) H_(22) O_(11)`, which resembles maltose in every respect except one: configuration of its glycosidic linkage.
Cellobiose, like maltose, is a reducing sugur, forms an osazone, exists in alpha and beta forms that undergo mutarotation and on acid-catalyzed hydrolysis, yields two molar equivalents of `D-(+)-` glucose. The sequence of oxidation (with `Br_(2)//H_(2) O)`, methylation (with `Me_(2) SO_(4), NaOH)` and hydrolysis `(H_(2) O, H^(+))` shows that `C1` of one glucose unit is connected in glycosidic linkage with `C4` of the other and that both rings are six membered.
`(+)-` Cellobiose differs from `(+)-` maltose in one respect: it is hydrolyzed by the enzyme emulsin (from bitter almonds), not by maltose, Since emulsion is known to hydrolyze only `beta`-glucoside linkages, we can conclude that the structue of `(+)-` cellobiose differs from that of `(+)-` maltose in only one resect: the D-glucose units are joined by a beta linkage rather than by an alpha linkage.