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

Question

BlackTom AI · Accepted Answer

First, let's restate the question for clarity: What type of point mutation leads to the introduction of a stop codon in the mRNA sequence?

Option 1: Missense. A missense mutation changes a single nucleotide so that one amino acid is replaced by a different one. While this alters the protein sequence, it does not inherently create a premature stop codon; its primary effect is at the level of amino acid substitution rather than termination.

Option 2: Frameshift. Frameshift mutations result from insertions or deletions that are not in multiples of three. They shift the reading frame of the entire downstream sequence, often creating a premature stop codon along the way, but the key characteristic is a shift in the reading frame rather than a single nucleotide substitution to a stop. It can lead to a stop codon, but this mutation type is defined by changing the reading frame, not by directly introducing a stop codon per se.

Option 3: Silent. Silent mutations alter the DNA sequence without changing the amino acid sequence of the resulting protein. This occurs due to redundancy in the genetic code, so no stop codon is introduced and protein function remains unchanged in terms of primary structure.

Option 4: Nonsense. A nonsense mutation is a single-nucleotide change that converts a codon encoding an amino acid into a stop codon, causing premature termination of translation. This directly matches the description of introducing a stop codon in the mRNA sequence.

In evaluating the options, consider the defining features of each mutation type. Missense changes amino acid identity but not termination; silent leaves the amino acid unchanged; frameshift alters the reading frame and can lead to early termination but the hallmark is frame disruption rather than a direct stop codon creation; the one that specifically creates a stop signal in the encoded protein is the nonsense mutation. The distinction hinges on whether the mutation directly creates a stop codon or affects reading frame rather than termination at a single codon.

Therefore, when focusing on the mechanism that introduces a stop codon directly, the option describing that exact effect aligns with the concept of a nonsense mutation.

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

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