Answer to Question #137057 in Genetics for Alidia

Question

In bacteria, researchers have isolated strains that carry
mutations within the tRNA genes. These mutations can
change the sequence of the anticodon. For example, a
normal tRNATrp gene would encode a tRNA with the
anticodon 3’-ACC-5’. A mutation could change this
sequence to 3’-CCC-5’. When this mutation occurs, the
tRNA still carries a tryptophan at its 3’ acceptor stem,
even though the anti-codon sequence has been altered.

A. How would this mutation affect the synthesis of
proteins within the bacterium?

B. What does this mutation tell you about the recognition
between tryptophanyl-tRNA synthetase and tRNATrp ?
Does the enzyme primarily recognize the anticodon or
not?

Answer 1

A. The mutant tRNA would recognize glycine codons in the mRNA but would put in the amino acid tryptophan where glycine was supposed to be in the polypeptide.

B. This mutation tells us that the aminoacyl-tRNA synthetase is primarily recognizing regions of the tRNA molecule other than the anticodon region. In summary, tryptophanyl-tRNA synthetase primarily recognizes other regions of the tRNATrp sequence other than the anticodon region. Incase aminoacyl-tRNA synthetases recognized only the anticodon region, we would expect glycyl-tRNA synthetase to recognize this mutant tRNA and attach glycine. That is not what happens.