Which of the following best describes an amino acid?

An amino acid is best described as a simple organic compound that contains both a carboxyl group (-COOH) and an amino group (-NH2). This structure gives amino acids the unique properties that are essential for their role in biological systems. The carboxyl group is acidic and can release hydrogen ions, while the amino group can act as a base, accepting hydrogen ions. This dual functionality allows amino acids to participate in various biochemical reactions.

Furthermore, amino acids serve as the building blocks of proteins, linking together through peptide bonds to form long chains that fold into specific three-dimensional shapes necessary for their function. Each of the 20 standard amino acids has a unique side chain or R group, which determines its characteristics and role in protein synthesis.

In contrast to amino acids, carbohydrates are primarily composed of sugars and starches, while lipids are fats and oils that do not contain amino and carboxyl groups. Therefore, the correct description accurately captures the essence of amino acids and their fundamental role in biology.