Question

Which specific linkage makes cellulose unsuitable for human digestion?

• A. $\alpha$-1,4 glycosidic linkage
• B. $\alpha$-1,6 glycosidic linkage
• C. $\beta$-1,4 glycosidic linkage
• D. $\beta$-1,6 glycosidic linkage

Hint:

{Starch} → $\alpha$-1,4 linkage (digestible)
{Cellulose} → $\beta$-1,4 linkage (indigestible in humans).

Answer 1

The Correct Option is C

Concept: Cellulose is a structural polysaccharide found in plant cell walls. It is composed of repeating units of glucose molecules. These glucose units are connected by $\beta$-1,4 glycosidic linkages. Humans lack the enzyme cellulase, which is required to break this type of bond. As a result, cellulose cannot be digested in the human digestive system and functions mainly as dietary fiber.
Step 1: Identify the linkage responsible for cellulose indigestibility.

• $\alpha$-1,4 linkage – Present in starch and digestible by humans.
• $\alpha$-1,6 linkage – Found in glycogen and starch branching.
• $\beta$-1,4 linkage – Present in cellulose and indigestible for humans.
• $\beta$-1,6 linkage – Not characteristic of cellulose structure.

Thus, the linkage responsible for the indigestibility of cellulose is the $\beta$-1,4 glycosidic linkage.