What is a nonsense mutation?

What is a nonsense mutation?

• A. A mutation that changes an amino acid codon to a stop codon.
• B. A mutation that changes a stop codon to an amino acid.
• C. A mutation that duplicates a codon.
• D. A mutation that inserts an extra amino acid.

Answer: (A)

A nonsense mutation is a change in a gene that converts a codon that normally specifies an amino acid into a stop codon, causing translation to terminate prematurely and producing a shortened protein. This premature stop signal truncates the polypeptide, often leading to loss of function or instability of the protein. That’s why this option is the best description: it captures the defining feature—the creation of a stop signal during protein synthesis. If the stop codon were changed to an amino acid, translation could continue longer than normal, which is the opposite effect. Duplicating a codon or inserting an extra amino acid adds residues but does not inherently introduce a premature stop, so they describe different mutation types.

A nonsense mutation is a change in a gene that converts a codon that normally specifies an amino acid into a stop codon, causing translation to terminate prematurely and producing a shortened protein. This premature stop signal truncates the polypeptide, often leading to loss of function or instability of the protein.

That’s why this option is the best description: it captures the defining feature—the creation of a stop signal during protein synthesis. If the stop codon were changed to an amino acid, translation could continue longer than normal, which is the opposite effect. Duplicating a codon or inserting an extra amino acid adds residues but does not inherently introduce a premature stop, so they describe different mutation types.