What distinguishes amino acids from other compounds?

Amino acids are unique compounds characterized by the presence of both a carboxyl group (-COOH) and an amino group (-NH2). This distinctive structure is what sets amino acids apart from many other organic molecules. The carboxyl group allows amino acids to act as acids, while the amino group gives them their basic (alkaline) properties.

Additionally, the presence of a variable side chain, known as the R group, attached to the central carbon atom provides diversity in amino acids, influencing their overall structure and function in proteins. This duality of functional groups is essential for the formation of proteins and is critical for biological processes.

In contrast, other options present characteristics that do not accurately define amino acids: they often contain additional elements like oxygen and sulfur, exhibit a range of energy content, and can feature both polar and non-polar side chains. Therefore, the correct choice highlights the unique functional groups common to all amino acids.