Question
Explain how a single base change in a gene could lead to premature termination of translation of the mRNA from that gene.
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A gene is a segment of DNA that contains the instructions for making a specific protein. This process involves transcription (where DNA is converted to mRNA) and translation (where mRNA is used to synthesize proteins). Show more…
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Genetically engineered mRNAs that code for a stretch of basic residues, such as poly(Lys), induce translation termination and destruction of the nascent polypeptide. Explain how this response would protect cells from the effect of faulty transcription that produces mRNAs with mutated Stop codons.
A mutation in DNA generates a UGA stop codon in the middle of the mRNA coding for a particular protein. A second mutation in the cell's DNA leads to a single nucleotide change in a tRNA that allows the correct translation of the protein; that is, the second mutation suppresses" the defect caused by the first. The altered tRNA translates the UGA as tryptophan. What nucleotide change has probably occurred in the mutant tRNA molecule? What consequences would the presence of such a mutant tRNA have for the translation of the normal genes in this cell?
A particular protein has the amino acid sequence $$N ... Ala-Pro-His-Trp-Arg-Lys-Gly-Val-Thr ... C$$ within its primary structure. A geneticist studying mutations affecting this protein discovered that several of the mutants produced shortened protein molecules that terminated within this region. In one of them, the His became the terminal amino acid. a. What DNA single-base change(s) would cause the protein to terminate at the His residue? b. What other potential sites do you see in the DNA sequence encoding this protein where mutation of a single base pair would cause premature termination of translation?
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