Which one of the following is a non-reducing carbohydrate?
- Maltose
- Sucrose
- Lactose
- Ribose 5-phosphate
Answer
(2) Sucrose
Solution
A sugar is reducing when it has a free aldehyde or ketone (hemiacetal) group.
⇒ Maltose and lactose have one free anomeric carbon, so they are reducing sugars.
⇒ Ribose 5-phosphate has a free aldehyde (anomeric) group, so it is reducing.
∵ In sucrose, the glycosidic bond joins C1 of glucose with C2 of fructose, both reducing groups are blocked.
∴ Sucrose is a non-reducing carbohydrate.
Answer: (2)