Structures of four disaccharides are given below. Among the given disaccharides, the non-reducing sugar is:
Structures of four disaccharides are given below. Among the given disaccharides, the non-reducing sugar is:
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- Maltose
- Lactose
- Sucrose
- Cellobiose
The Correct Option is C
Solution and Explanation
Concept: Reducing sugars are those which have a free anomeric carbon atom (free \(-OH\) group on the hemiacetal carbon) that can open up to form an aldehyde or ketone group, allowing them to reduce reagents like Tollen’s or Fehling’s solution. Non-reducing sugars lack a free anomeric carbon because both anomeric carbons are involved in glycosidic linkage.
Step 1: Analyze each disaccharide.
- \(\mathbf{Maltose}\): Formed from two glucose units with \(\alpha(1 \to 4)\) linkage. One anomeric carbon is free → reducing sugar.
- \(\mathbf{Lactose}\): Formed from glucose and galactose with \(\beta(1 \to 4)\) linkage. One anomeric carbon is free → reducing sugar.
- \(\mathbf{Sucrose}\): Formed from glucose and fructose with \(\alpha(1 \to 2)\) and \(\beta(2 \to 1)\) linkage. Both anomeric carbons are involved in glycosidic bond → non-reducing sugar.
- \(\mathbf{Cellobiose}\): Formed from two glucose units with \(\beta(1 \to 4)\) linkage. One anomeric carbon is free → reducing sugar.
Step 2: Conclusion. Among the given disaccharides, sucrose is the only non-reducing sugar. \[ \text{Answer: Sucrose (Option 3)} \]
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