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BIO NMDCAT Structure of DNA
nmdcat.online July 3, 2026

98. A mutation alters the conserved Shine-Dalgarno sequence upstream of a bacterial structural gene. When this mutated polycistronic mRNA interacts with prokaryotic translation machinery, the immediate molecular outcome is the

A. Failure of the small (30S) ribosomal subunit to correctly align with the start codon
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B. Accelerated transcription of downstream regulatory genes
C. Spontaneous excision of the mutated sequence by the spliceosome
D. Direct methylation of the structural gene's promoter region

📝 Explanation

The Shine-Dalgarno sequence base-pairs with the 16S rRNA of the 30S subunit, aligning the bacterial ribosome with the start codon to initiate translation.

📖 Additional Information

  • Failure of the small (30S) ribosomal subunit to correctly align with the start codon
  • Accelerated transcription of downstream regulatory genes
  • Spontaneous excision of the mutated sequence by the spliceosome
  • Direct methylation of the structural gene's promoter region

The Shine-Dalgarno sequence base-pairs with the 16S rRNA of the 30S subunit, aligning the bacterial ribosome with the start codon to initiate translation.

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