Final answer:
Tryptophan (Trp) is the amino acid that is coded by only one codon, which is UGG. The genetic code is generally redundant but tryptophan and methionine are both coded by a single codon each.
Step-by-step explanation:
Among the amino acids listed, tryptophan (Trp) is the one that is coded by only one codon. The genetic code is unambiguous and redundant, meaning each codon specifies one amino acid, and most amino acids are encoded by more than one codon. However, tryptophan and methionine are exceptions to this redundancy, as they each have a single codon.
The codon for tryptophan is UGG, and it is the only mRNA codon that codes for tryptophan. Methionine (Met) is also coded by a single codon (AUG), which also serves as the initiation or start codon for protein synthesis. In contrast, codons such as UUU for phenylalanine and GGU, GGC, GGA, GGG for glycine showcase the redundancy with multiple codons coding for the same amino acid.