Advanced Placement (AP) Biology Practice Exam

What is true about the structure of triacylglycerols?

1. They consist of two fatty acid chains

2. They are made of three fatty acid chains linked to a sterol

3. They contain three fatty acid chains linked to a glycerol

4. They have a continuous chain of fatty acids

The correct answer is: They contain three fatty acid chains linked to a glycerol

Triacylglycerols, also known as triglycerides, are composed of three fatty acid chains that are esterified to a single glycerol molecule. This structure is fundamental in understanding how triacylglycerols function in biological systems. The glycerol serves as the backbone, and the fatty acids can vary in length and degree of saturation, influencing the properties of the fat, such as whether it is solid or liquid at room temperature. This unique structure allows triacylglycerols to efficiently store energy in adipose tissue, where they can deliver a significant energy yield upon hydrolysis. Their hydrophobic nature also means they are not soluble in water, making them ideal storage molecules in organisms. The other answer choices misrepresent the structure of triacylglycerols. For instance, they do not consist of just two fatty acid chains or link fatty acids to a sterol; instead, they require three fatty acid chains to form a complete triglyceride structure.