The sixth codon from an mRNA transcript(makes peptide A) is5\'...CUU...3\', whic

Question

The sixth codon from an mRNA transcript(makes peptide A) is5'...CUU...3', which is translated as leucine. The anticodon of theleucyl tRNA correctly base-paired to the mRNA transcript codon is3'...GAA..5'.

codon: 5'...CUU...3'

anticodon: 3'...GAA...5'

Now the part I need help with:

Surprisingly, the sixth amino acid in peptide A is found to bePhenylalanine instead of the expect leucine. Assuming thataminoacylation by tRNA synthetase is unchanged in this cell, howdoes a single mutation in the tRNA gene give this outcome?(notethat the mutation happens in the tRNA gene not the gene/mRNAtranscript of peptide A)

What specifically has changed to allow the anomalous outcomedescribed above?

I was thinking that a single point mutation happened on the tRNAgene, changing the GAA anticodon to AAG but I don't think this isright because this would mean that the 5/3 prime ends of thechanged/mutated anticodon would not match the codon of the mRNAtranscript.

For example, the mutation resulted in the anticodon3'...AAG...5' but the codon is 5'...CUU...3'.

Explanation / Answer

      You are right to thinkthat there occurred a point mutation.       The type of point mutationthat has occurred is a transition where a purine is replaced by another purine, that is in the       t-RNA at 3' positioninstead of G there is A.       As mentioned that theamino acylation in the t-RNA is unchanged, (which means it carriedphenyalanine only instead of       leucine) and the mutationis in t-RNA and not in m-RNA, the most possible point mutation istransition which has       replaced G (A ispresent).       Your thought that GAA haschanged to AAG wont be right because it wont be a pointmutation and the direction also        will bedifferent.       

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