Which of the following is an example of an amino acid?

The correct choice is isoleucine, which is indeed an example of an amino acid. Amino acids are organic compounds characterized by having both an amino group (-NH2) and a carboxyl group (-COOH), along with a specific side chain unique to each amino acid. Isoleucine is one of the essential amino acids, meaning the body cannot synthesize it and it must be obtained from the diet. It plays a crucial role in protein synthesis and various metabolic processes.

On the other hand, serine is also an amino acid, so that could be another potential correct answer if the question allows for more than one choice. Cholesterol and glucose, however, are not amino acids. Cholesterol is a type of lipid important for cellular structure and signaling, and glucose is a simple sugar and a primary energy source for cells. Understanding the classification of these biomolecules and their structures is important for grasping fundamental biochemical concepts.