What group do negatively-charged amino acids belong to?

Negatively-charged amino acids are classified as anionic. This classification comes from their side chains, which contain carboxyl groups that can donate a proton, giving rise to a negative charge at physiological pH. This charge not only influences their behavior in biochemical reactions but also affects how these amino acids interact with other molecules, such as enzymes or substrates, and with water.

In contrast, cationic amino acids carry a positive charge due to the presence of amino groups, polar amino acids have side chains that can form hydrogen bonds and are typically neutral, while nonpolar amino acids have hydrophobic side chains that do not carry any charge. Thus, the unique properties of anionic amino acids, including their charge and interactions, solidly place them within the anionic group.