Figure 1.

Examples of the continuous numbering of atoms in amino acid molecules: (a) tyrosine ((2S)-2-amino-3-(4-hydroxyphenyl)propanoic acid); (b) 3-hydroxyproline ((2S,3S)-3-hydroxypyrrolidine-2-carboxylic acid); (c) arginine ((2S)-2-amino-5-carbamimidamidopentanoic acid); (d) histidine ((2S)-2-amino-3-(1H-imidazol-5-yl)propanoic acid); (e) tryptophan ((2S)-2-amino-3-(1H-indol-3-yl)propanoic acid); (f) (2S)-2-amino-3-(4-ethoxy-2-ethylphenyl)propanoic acid. Figure prepared using Marvin Sketch editor (Chem Axon, Budapest, Hungary).