(define codon->aminoAcid
  (lambda (codon)
    (case codon
      (("GCT" "GCC" "GCA" "GCG") 'alanine)
      (("CGT" "CGC" "CGA" "CGG" "AGA" "AGG") 'arginine)
      (("GAT" "GAC") 'aspartic_acid)
      (("TGT" "TGC") 'cysteine)
      (("CAA" "CAG") 'glutamine)
      (("GGT" "GGC" "GGA" "GGG") 'glycine)
      (("CAT" "CAC") 'histidine)
      (("ATT" "ATC" "ATA") 'isoleucine)
      (("TTA" "TTG" "CTT" "CTC" "CTA" "CTG") 'leucine)
      (("AAA" "AAG") 'lysine)
      (("ATG" 'methionine))
      (("TTT" "TTC") 'phenylalanine)
      (("CCT" "CCC" "CCA" "CCG") 'proline)
      (("TCT" "TCC" "TCA" "TCG" "AGT" "AGC") 'serine)
      (("ACT" "ACC" "ACA" "ACG") 'threonine)
      (("TGG") 'tryptophan)
      (("TAT" "TAC") 'tyrosine)
      (("GTT" "GTC" "GTA" "GTG") 'valine)
      (("UAG" "UGA" "UAA") (error 'codon->aminoAcid "You supplied a stop codon."))
      )))