Which type of mutation introduces a premature stop codon?

Which type of mutation introduces a premature stop codon?

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

Answer: (C)

Mutations that create a stop signal within the coding sequence are known as nonsense mutations. In protein synthesis, the genetic code uses three stop codons to end translation. If a single nucleotide change converts a normal codon into one of these stop signals, ribosomes halt early and the resulting protein is shortened, often nonfunctional or unstable. This is distinct from missense mutations, which change the amino acid specified by a codon, or silent mutations, which do not alter the amino acid due to codon redundancy. Frameshift mutations involve adding or removing nucleotides that shift the reading frame and can also lead to premature termination, but the mechanism is different—it's the shift itself that alters many downstream codons, not a single codon turning into a stop codon.

Mutations that create a stop signal within the coding sequence are known as nonsense mutations. In protein synthesis, the genetic code uses three stop codons to end translation. If a single nucleotide change converts a normal codon into one of these stop signals, ribosomes halt early and the resulting protein is shortened, often nonfunctional or unstable. This is distinct from missense mutations, which change the amino acid specified by a codon, or silent mutations, which do not alter the amino acid due to codon redundancy. Frameshift mutations involve adding or removing nucleotides that shift the reading frame and can also lead to premature termination, but the mechanism is different—it's the shift itself that alters many downstream codons, not a single codon turning into a stop codon.