Which of the following carbohydrates is a non-reducing disaccharide that yields D-glucose and D-fructose upon enzymatic hydrolysis?
Answer and explanation
Correct answer: A. Sucrose
- Step 1: A reducing sugar possesses a free or potentially free anomeric hemiacetal or hemiketal group capable of reducing cupric ions.
- Step 2: In sucrose, the reducing anomeric carbon of -D-glucopyranose is linked directly to the reducing anomeric carbon of -D-fructofuranose via an glycosidic bond.
- Step 3: Because both anomeric carbons are engaged in the glycosidic bond, sucrose has no free aldehyde/ketone group and is non-reducing.
Answer
Sucrose.
Why not the others: Maltose is a reducing disaccharide of two glucose units (); Lactose is a reducing disaccharide of galactose and glucose (); Cellobiose is a reducing disaccharide of two glucose units ().
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