AAMC FL Practice Exam

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Study for the AAMC FL Exam. Prepare with comprehensive flashcards and multiple-choice questions, each equipped with hints and explanations. Gear up for your medical school entrance exam!

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Which of the following is NOT a reducing sugar?

Glucose
Sucrose
Lactose
Fructose

The correct answer is: Sucrose

A reducing sugar is any sugar that can donate electrons to another chemical species, which is typically determined by its ability to reduce certain agents and is usually characterized by the presence of a free aldehyde or ketone group in its structure. In the case of sucrose, it is a disaccharide composed of glucose and fructose, and it features a glycosidic bond that links these two monosaccharides. This bond forms between the aldehyde group of glucose and the hydroxyl group of fructose, effectively blocking the aldehyde group of glucose from being available to participate in redox reactions. Consequently, sucrose does not have any free aldehyde or ketone functional groups available to act as a reducing agent, which is why it is categorized as a non-reducing sugar. On the other hand, glucose, lactose, and fructose each have free carbonyl groups that are capable of acting as reducing agents; thus, they can reduce other substances in chemical reactions. This makes them classified as reducing sugars.