Which mutation is most likely to truncate the polypeptide?

Which mutation is most likely to truncate the polypeptide?

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

Answer: (B)

A nonsense mutation directly creates a stop codon in the mRNA, so the ribosome stops translating sooner than it should. That immediate signal to terminate leads to a polypeptide that is shorter than normal, i.e., truncated. Missense changes one amino acid but doesn’t stop translation. Silent mutations don’t change the amino acid at all. Frameshift mutations shift the reading frame and can cause a premature stop downstream, but whether a stop occurs quickly depends on the new sequence, so it’s less consistently truncating than a direct stop codon.

A nonsense mutation directly creates a stop codon in the mRNA, so the ribosome stops translating sooner than it should. That immediate signal to terminate leads to a polypeptide that is shorter than normal, i.e., truncated.

Missense changes one amino acid but doesn’t stop translation. Silent mutations don’t change the amino acid at all. Frameshift mutations shift the reading frame and can cause a premature stop downstream, but whether a stop occurs quickly depends on the new sequence, so it’s less consistently truncating than a direct stop codon.