Which of the following statements about nonsense mutations is correct?

• A. Nonsense mutations change an amino acid to another amino acid.
• B. Nonsense mutations always lead to a longer protein.
• C. Nonsense mutations do not affect protein synthesis.
• D. Nonsense mutations result in a premature stop codon.

Answer: (D)

Verified step by step guidance

1. Understand what a nonsense mutation is: A nonsense mutation is a type of point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon, in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product.
2. Identify the role of stop codons: In the genetic code, stop codons signal the termination of protein synthesis. The three stop codons are UAA, UAG, and UGA.
3. Analyze the effect of a nonsense mutation: When a nonsense mutation occurs, it changes a codon that specifies an amino acid into a stop codon. This leads to the termination of translation earlier than expected, resulting in a shorter protein.
4. Evaluate the given statements: The statement 'Nonsense mutations result in a premature stop codon' is correct because it accurately describes the effect of a nonsense mutation on the genetic code and protein synthesis.
5. Consider the implications: Since nonsense mutations lead to a premature stop codon, they typically result in a nonfunctional protein, which can have significant effects on an organism's phenotype and can be associated with various genetic disorders.