Question

Which of the following saccharides contain $\beta$-D-glucose units?

• A. II, IV
• B. II, III
• C. I, III
• D. I, IV

Hint:

{Starch/Glycogen} $\rightarrow$ $\alpha$-D-Glucose (Digestible). {Cellulose} $\rightarrow$ $\beta$-D-Glucose (Indigestible by humans).

Answer 1

The Correct Option is B

Step 1: Analyze Monomer Units and Linkages:
I. Sucrose: $\alpha$-D-Glucose + $\beta$-D-Fructose. (Linkage: $C1-C2$).
II. Lactose: $\beta$-D-Galactose + $\beta$-D-Glucose. (Linkage: $\beta-1,4$). Contains $\beta$-D-glucose.
III. Cellulose: Polymer of $\beta$-D-Glucose. (Linkage: $\beta-1,4$). Purely $\beta$-D-glucose units.
IV. Amylose (Starch): Polymer of $\alpha$-D-Glucose. (Linkage: $\alpha-1,4$).

Step 2: Selection:
Lactose and Cellulose contain $\beta$-D-Glucose units. This corresponds to II and III.