Advanced Placement (AP) Biology Practice Exam

What is the basic structural formula for sugars?

1. They contain amino groups and phosphate groups.

2. They feature a carbonyl group and multiple hydroxyl groups.

3. They are made only of carbon and hydrogen.

4. They lack any defined structural features.

The correct answer is: They feature a carbonyl group and multiple hydroxyl groups.

The basic structural formula for sugars, which are classified as carbohydrates, indeed features a carbonyl group and multiple hydroxyl groups. Sugars can exist in various forms, including monosaccharides like glucose and fructose, which typically have a carbonyl group (either as an aldehyde or a ketone) and numerous hydroxyl (-OH) groups attached to their carbon backbone. This structure is crucial because it not only defines the properties and reactivity of sugars but also enables them to form rings and polymerize into larger carbohydrates, such as disaccharides and polysaccharides. In biological contexts, the presence of both carbonyl and hydroxyl groups plays a vital role in the solubility of sugars in water and their participation in various metabolic pathways. This structural characteristic allows for interactions with other molecules, making sugars essential for energy storage, cell structure, and as important signaling molecules in biological systems.