Q.84
Which part of the ribosome identifies the Shine – Dalgarno sequence?
(1) Protein
(2) 16S rRNA
(3) 23S rRNA
(4) 5S rRNA
- Shine-Dalgarno Sequence Recognition: The Shine-Dalgarno (SD) sequence is a conserved polypurine motif (consensus $5'\text{-AGGAGG-}3'$) located 8–10 nucleotides upstream of the start codon ($AUG$) on prokaryotic mRNA.
- Role of 16S rRNA: The $3'$ end of the 16S rRNA component of the prokaryotic small ($30\text{S}$) ribosomal subunit contains a complementary polypyrimidine sequence ($5'\text{-ACCUCCU-}3'$, anti-Shine-Dalgarno sequence).
- Mechanism: Base-pairing between the SD sequence and the 16S rRNA aligns the mRNA initiator codon precisely at the ribosomal P-site for initiation complex formation.
- Other rRNAs:
- 23S rRNA: Large ($50\text{S}$) subunit component containing peptidyl transferase ribozyme activity.
- 5S rRNA: Large subunit structural stabilizer.
Correct option: (2) 16S rRNA
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