• 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

• Stop Codons (Termination Codons): In the standard genetic code, three codons do not encode any amino acid and serve as translational stop signals:

• UAA (Ochre)
• UAG (Amber)
• UGA (Opal)
  • Evaluation of Options:

• UAG: Amber stop codon.
• UAA: Ochre stop codon.
• Both UAG and UAA trigger release factors (RF1/RF2 in prokaryotes; eRF1 in eukaryotes) to hydrolyze the peptidyl-tRNA bond and release the nascent polypeptide chain.
• Non-Termination Codons:
• UUU: Encodes Phenylalanine (Phe).
• GUG: Encodes Valine (Val); acts as an alternative initiation codon in prokaryotes.

• Central Dogma of Molecular Biology: Proposed by Francis Crick in 1958 (and reaffirmed in Nature in 1970).
• Core Principle: Explains the directional, irreversible flow of sequential genetic information in biological systems:

• Postulate: Once "information" has passed into protein, it cannot get out again (protein sequence cannot direct nucleic acid synthesis).

Correct option: (2) Francis Crick