AAMC FL Practice Exam

Which of the following best describes glycerol?

1. A 3 carbon chain with 3 hydroxyl groups

2. A 4 carbon chain with 2 hydroxyl groups

3. A hydrocarbon with a carboxyl group

4. A simple sugar molecule

The correct answer is: A 3 carbon chain with 3 hydroxyl groups

Glycerol is accurately described as a three-carbon chain (trihydroxy alcohol) that contains three hydroxyl (-OH) groups. The structure of glycerol consists of three carbon atoms that are sequentially connected, with each carbon bonded to a hydroxyl group, making it a polyol. This configuration is crucial as it determines glycerol's properties and functions, particularly its role in lipid metabolism where it serves as a backbone for triglycerides and phospholipids. Other descriptions provided in the options do not align with the molecular characteristics of glycerol. For instance, a four-carbon chain with two hydroxyl groups does not fit the chemical structure of glycerol. Similarly, a hydrocarbon with a carboxyl group refers to compounds like fatty acids, and a simple sugar molecule generally relates to monosaccharides, which are different in structure and function compared to glycerol. Thus, the correct characterisation of glycerol confirms its unique structure and significance in biological processes.