The 20 naturally occurring amino acids (See the following table) are all l amino acids, and they all have the S configuration, with the exception of glycine (which lacks a chirality center) and cysteine. Naturally occurring cysteine is an l amino acid, but it has the R configuration. Explain.

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Abbreviation Name Structure Abbreviation Name Structure Amino acids with polar side chains Amino acids with nonpolar si de chalns н. HN. Glycine Gly G Asparagine Asn N он NH2 NH2 Gin Q Glutamine H2N Он H3C. Alanine Ala A Он NH2 NH2 Ser S Seine но он NH2 Valine Val v он он NH2 Threonine Thr T он NH3 он Leu L Leucine Tyr Y Туюaine он NH2 NH2 Cysteine Cys C HS он Isoleucine De I OH NH2 NH2 Amino acids with acidic side chains но. Aspartic acid Asp D он Methionine Met M Он NH2 NH2 Glưamic acid Giu E но он он NH2 Pro P Proline NH Amino acids with basic side chains Arg R Arginine он Phenylalanine он Phe F NH2 NH2 Histidine His H он NH2 NH он Trр W Tryptophan NH2 H2N. Lysine Lys K он NH2