AAMC FL Practice Exam

Which of the following is true regarding reducing sugars?

1. They can form aldehydes

2. They always contain three or more carbon atoms

3. They consist solely of saturated molecules

4. They cannot undergo oxidation

The correct answer is: They can form aldehydes

Reducing sugars are a type of carbohydrate that have the ability to act as reducing agents because they contain free aldehyde or ketone groups. This characteristic allows them to participate in redox reactions, specifically by reducing other compounds while themselves being oxidized. When a reducing sugar is in solution, conditions may allow these carbonyl groups to exist in their open-chain form, which can then convert into aldehyde structures. This open-chain form is crucial for the reaction where the sugar donates electrons to another molecule, demonstrating its capacity to form aldehydes. Hence, stating that reducing sugars can form aldehydes aligns with the chemical properties of these compounds. The other options do not hold true in the context of reducing sugars. For example, while many reducing sugars may have three or more carbon atoms, there are also reducing sugars with fewer, such as glyceraldehyde (which contains three carbon atoms). Reducing sugars can also include both saturated and unsaturated forms, as the definition does not restrict to saturation. Furthermore, all reducing sugars are characterized by their ability to undergo oxidation, which is the fundamental aspect that defines them. Thus, recognizing that reducing sugars can form aldehydes accurately captures an essential property of these carbohydrates.