The presence of what type of side chain characterizes the amino acids with nonpolar, nonaromatic properties?

The presence of hydrophobic side chains characterizes amino acids with nonpolar, nonaromatic properties. These side chains are typically composed of hydrocarbons or other structures that do not interact favorably with water, making them nonpolar. Nonpolar, nonaromatic amino acids tend to aggregate in the interior of proteins, away from the aqueous environment, which contributes to the overall stability and structure of proteins.

In contrast, hydrophilic side chains are associated with interactions in polar environments, charged side chains interact with other charged molecules and water, and polar side chains contain functional groups that can readily form hydrogen bonds with water. Therefore, the hydrophobic nature of the side chains in nonpolar, nonaromatic amino acids is what distinctly classifies them and influences their behavior in biological systems.