Which mutation type introduces a premature stop codon?

Which mutation type introduces a premature stop codon?

• A. Nonsense mutation
• B. Missense mutation
• C. Silent mutation
• D. Frameshift mutation

Answer: (A)

A premature stop codon occurs when translation is halted earlier than normal, yielding a shorter, usually nonfunctional protein. A nonsense mutation is the change that directly causes this: a single nucleotide substitution converts a codon that normally codes for an amino acid into one of the stop codons (UAA, UAG, or UGA). Because the ribosome stops at this new stop codon, part of the polypeptide is never made, which often severely disrupts protein function. In contrast, a missense mutation changes one amino acid to another but does not create a stop signal; a silent mutation changes the DNA without altering the amino acid sequence; and a frameshift mutation shifts the reading frame by inserting or deleting nucleotides, which can produce a premature stop downstream but does so through a different mechanism than directly converting a codon to a stop.

A premature stop codon occurs when translation is halted earlier than normal, yielding a shorter, usually nonfunctional protein. A nonsense mutation is the change that directly causes this: a single nucleotide substitution converts a codon that normally codes for an amino acid into one of the stop codons (UAA, UAG, or UGA). Because the ribosome stops at this new stop codon, part of the polypeptide is never made, which often severely disrupts protein function.

In contrast, a missense mutation changes one amino acid to another but does not create a stop signal; a silent mutation changes the DNA without altering the amino acid sequence; and a frameshift mutation shifts the reading frame by inserting or deleting nucleotides, which can produce a premature stop downstream but does so through a different mechanism than directly converting a codon to a stop.