Question

A nonsense mutation involves the creation of a an -

• A. Regulatory site
• B. AG splice acceptor site
• C. Stop codon
• D. Different amino acids

Hint:

Nonsense mutations often trigger a cellular surveillance pathway called Nonsense-Mediated Decay (NMD), which selectively degrades mRNA transcripts containing premature stop codons to prevent the accumulation of toxic truncated proteins.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Point mutations are single-nucleotide changes in genomic DNA that can alter the corresponding mRNA codon during transcription and translation.
These mutations are classified based on their functional impact on the resulting polypeptide chain.

Step 2: Detailed Explanation:
A nonsense mutation is a specific type of point mutation where a single base substitution changes a codon that specifies an amino acid into a premature termination (stop) codon.
The three standard stop codons in the universal genetic code are UAG (amber), UAA (ochre), and UGA (opal).
When the ribosome encounters this premature stop codon during translation, translation is terminated prematurely, releasing an incomplete, truncated, and usually non-functional polypeptide.
Let us compare this with the other options:
- A missense mutation changes a codon to specify a different amino acid.
- Mutations at splice sites alter the highly conserved dinucleotides (such as the AG splice acceptor site) at intron-exon boundaries, leading to splicing errors.
- Regulatory site mutations occur in non-coding promoter or enhancer regions, affecting the rate of transcription rather than the translation of the polypeptide itself.

Step 3: Final Answer:
A nonsense mutation results in the creation of a premature stop codon, which corresponds to option (C).