How do silent, missense, and nonsense mutations differ?

• A. Silent mutations do not change the amino acid; missense mutations change one amino acid; nonsense mutations introduce a premature stop codon.
• B. Silent mutations change the amino acid sequence.
• C. Nonsense mutations change a single amino acid.
• D. Missense mutations create a frameshift.

Answer: (A)

In DNA, single-nucleotide changes can affect the protein in distinct ways based on how the genetic code uses codons to specify amino acids. A silent mutation is when the DNA change does not alter the amino acid that a codon encodes because multiple codons can code for the same amino acid. The protein sequence stays the same, even though the DNA sequence has changed, so these mutations are usually neutral for the protein's function (though they can sometimes affect gene expression or RNA processing in rare cases).

A missense mutation occurs when a single base change changes one codon to code for a different amino acid. This alters the protein’s amino acid at that position, and the effect depends on how different the new amino acid is and where it appears in the protein—some changes are minor, others can seriously disrupt structure or activity.

A nonsense mutation is when a single base change turns a codon that encodes an amino acid into a stop codon, causing translation to terminate early. The resulting protein is truncated and often nonfunctional.

These distinctions are what the choice captures: silent mutations don’t change the amino acid; missense mutations change one amino acid; nonsense mutations create a premature stop. The other statements mix up these effects—silent mutations do change the amino acid, nonsense mutations don’t replace an amino acid with another but introduce a stop, and frameshifts come from insertions or deletions rather than simple substitutions that cause missense.