A researcher is studying a mutant gene where the codon AAA (lysine) has been changed to UAA at position 150 of a 400-amino-acid protein. The resulting protein is only 149 amino acids long. Which type of mutation has occurred?
- A Nonsense (stop) mutation ✓
- B Missense mutation
- C Silent (synonymous) mutation
- D Frameshift mutation
Correct answer: A. Nonsense (stop) mutation
Explanation
UAA is one of the three stop codons (UAA, UAG, UGA). Converting the sense codon AAA (lysine) to UAA introduces a premature stop codon, terminating translation at position 149 and producing a truncated 149-amino-acid protein. This is a nonsense mutation, which is a single-nucleotide substitution that converts an amino-acid codon into a termination codon. It typically produces a loss-of-function effect.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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