Triglycerides are composed of glycerol and fatty acids. Which of the following best describes triglycerides?

• A. Glycerol with three fatty acids
• B. Glycerol with two fatty acids
• C. Three glucose molecules
• D. One glycerol with one fatty acid

Answer: (A)

Triglycerides store energy by building a glycerol backbone with three fatty acids attached. The word “tri” signals three attachments, and the bonds form when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids, making three ester bonds. That’s why the description with glycerol plus three fatty acids is the correct one. If there were only two fatty acids, it would be a diacylglycerol; with one fatty acid, a monoacylglycerol. Three glucose molecules would describe a carbohydrate, not a lipid.