Which of the following is most likely to alter or eliminate the transcription of a gene?
Group of answer choices
A A nucleotide substitution in the first exon of the gene.
B A large deletion in the first exon of the gene.
C A nucleotide substitution that alters the translation initiation codon.
D None of the other answers are correct, which makes this the best answer
The correct answer and explanation is:
The correct answer is C: A nucleotide substitution that alters the translation initiation codon.
Explanation:
Transcription is the process by which a gene is copied into RNA, and this RNA is later used for translation into a protein. For transcription to occur correctly, a gene must have several important regulatory elements, such as the promoter region and the proper initiation codon for translation.
- Option A: A nucleotide substitution in the first exon of the gene
A substitution in the first exon can potentially alter the amino acid sequence of the resulting protein, but it does not necessarily affect the transcription process itself. Exonic mutations are more likely to affect the protein’s function or structure once translation occurs, rather than the ability of the gene to be transcribed. - Option B: A large deletion in the first exon of the gene
A large deletion in the first exon might result in a loss of part of the gene’s coding sequence or disrupt the reading frame, but the gene could still be transcribed. However, the final protein product may be incomplete or nonfunctional. A deletion could affect transcription efficiency if it impacts important regulatory regions, but in isolation, this option is not as impactful as a mutation in the translation initiation codon. - Option C: A nucleotide substitution that alters the translation initiation codon
This is the most likely to affect or eliminate transcription. The translation initiation codon, typically “AUG” (in eukaryotes), is essential for starting protein synthesis. If this codon is altered, translation cannot begin properly. In some cases, such a mutation might not directly prevent transcription but will render the mRNA nonfunctional for protein production, essentially eliminating its biological effect. It can also indirectly affect the process if it causes the ribosome to not recognize the mRNA. - Option D: None of the other answers are correct, which makes this the best answer
This is not correct because option C clearly identifies a situation that would most likely alter or eliminate the transcription of a gene.
Therefore, option C, a nucleotide substitution that alters the translation initiation codon, would be the most likely to alter or eliminate gene transcription.