Why amino acid is technically not an amino acid?

Answer 1

An amino acid is typically defined as a molecule containing both an amine group (-NH2) and a carboxylic acid group (-COOH), along with a specific side chain (R group) that distinguishes one amino acid from another. However, some compounds that are referred to as amino acids may lack one of these functional groups or do not fit the traditional definition due to structural variations. For example, compounds like taurine contain a sulfonic acid group instead of a carboxylic acid, which may lead to the perception that they are not "true" amino acids despite their name. Thus, not all substances labeled as amino acids fully adhere to the classic definition.