The chemical properties of the R-groups obviously dominate the primary chemical differences between AAs. The chemical properties of the AA R-groups also dominate the chemical contribution an AA residue makes to the overall chemistry of a polypeptide or protein assembled from a given sequence of AAs. Thus, it is useful to consider the fundamental physical or chemical properties of the R-groups themselves. Classifying AAs according to the fundamental physical characteristics of their R-groups results in three basic physical categories -- nonpolar, neutral polar, and charged polar. The individual AAs representing each of these groupings are found in the tables below:

AA classification according to specific R-group chemical properties:

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