Which mutation describes a change of a single amino acid in a protein?

• A. Substitution
• B. Insertion
• C. Deletion
• D. Translocation

Answer: (A)

A single amino acid change in a protein typically arises from a nucleotide substitution that changes a codon to a different codon encoding a different amino acid. This missense mutation alters just one amino acid in the polypeptide, leaving the rest of the reading frame intact. Insertion or deletion mutations often shift the reading frame, causing many downstream amino acids to change (a frameshift), or introduce premature stop signals, so they don’t produce just one altered amino acid. Translocations involve moving larger DNA segments between chromosomes and affect multiple genes or regions, not a single codon in a single protein. Because a substitution can specifically alter one codon to code for a different amino acid, it best describes a change of a single amino acid in the protein.