This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Glucose is conveed to sorbitol by 
Select and explain. 
A. Aldolase B, B. Aldose reductase, C. Sorbitol Dehydrogenase, D. UDP galactose 4 epimerase
B: Aldose reductase
Answer: B: Aldose reductase 
Explanation: In lens, the enzyme aldose reductase reduces monosaccharides to corresponding sugar alcohols; glucose to sorbitol and galactose to galactitol. POLYOL PATHWAY OF GLUCOSE - Sorbitol is very poorly absorbed from intestine. It involves the reduction of glucose by aldose reductase to sorbitol, which can then be oxidized to fructose. This would amount to the interconversion of glucose to fructose. Glucose when conveed to sorbitol, cannot diffuse out of the cell easily and gets trapped there. Sorbitol is normally present in lens of eyes. But in diabetes mellitus, when glucose level is high, the sorbitol concentration also increases in the lens. This leads to osmotic damage of the tissue and development of cataract. Galactitol also causes cataract. REF: DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY, SIXTH EDITION, PG.NO.,119,588.