In a mutant strain of E. coli, a tRNA that recognizes the codon 5′ CUG 3′ of normal cells has a point mutation so that it now recognizes the codon 5′ GUG 3′ while still carrying its original amino acid. Surprisingly, a missense mutation found in a protein-coding gene is no longer causing problems for the cell due to the presence of this mutant tRNA.

a. What amino acid is this tRNA carrying?

b. Before the missense mutation in the protein-coding gene, what was the original encoded amino acid?

c. Before the change in the tRNA gene, what missense amino acid was incorporated in protein?