What type of point mutation leads to the introduction of a stop codon in mRNA sequence?

Question

BlackTom AI · Accepted Answer

To tackle the question, we first identify what a stop codon introduction means for a protein-coding sequence.
Option 1: Missense. This type of mutation changes one amino acid to another, but it does not create a premature stop codon, so the protein length may be altered but not necessarily shortened by a stop signal.
Option 2: Nonsense. This is the classic type of point mutation that changes a codon for an amino acid into a stop codon, causing premature termination of translation and producing a truncated, usually nonfunctional protein.
Option 3: Silent. A silent mutation alters the DNA sequence without changing the encoded amino acid due to redundancy in the genetic code; therefore no stop codon is introduced and the protein sequence remains unchanged.
Option 4: Frameshift. Frameshift mutations arise from insertions or deletions not in multiples of three, shifting the reading frame. While frameshifts can create premature stops downstream, they are not typically categorized as point mutations, and the crucial point of the question—a single-nucleotide change that directly generates a stop codon—points toward nonsense rather than frameshift.
In summary, the mutation type that directly introduces a stop codon through a single nucleotide change is the nonsense mutation, whereas the other options fail to match this specific mechanism because they either alter amino acids without creating a stop, leave the amino acid sequence unchanged, or involve a reading-frame disruption rather than a direct stop codon creation.

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What type of point mutation leads to the introduction of a stop codon in mRNA sequence?

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