What forms when the carboxyl group of a fatty acid combines with a hydroxyl group of glycerol?

When the carboxyl group of a fatty acid reacts with a hydroxyl group of glycerol, an ester bond is formed. This reaction is a key step in the creation of triglycerides, which consist of glycerol bonded to three fatty acid molecules. The carboxyl group, which contains a carbon atom double-bonded to an oxygen atom (C=O) and single-bonded to a hydroxyl group (-OH), reacts with the hydroxyl group of glycerol, resulting in the release of a water molecule (a process known as condensation or dehydration synthesis).

The resulting bond, known as an ester bond, links the fatty acid to the glycerol backbone, creating a structure that is essential for storing energy and forming cell membranes in biological systems. This is a fundamental concept in biochemistry, particularly in understanding how lipids are formed and function within living organisms. Other types of bonds mentioned in the choices, such as glycosidic and peptide bonds, serve different roles in carbohydrate and protein chemistry, respectively, and do not apply in the context of fatty acid and glycerol interactions.