In case of prokaryotes, the start codon is usually preceded by a sequence complementary to the
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- 16S rRNA
- 5S rRNA
- 28S rRNA
- 18S rRNA
The Correct Option is A
Solution and Explanation
Step 1: Translation initiation in prokaryotes
In prokaryotes, translation begins when the ribosome assembles at the start codon (AUG) on the mRNA. However, efficient recognition of the start codon requires a special upstream sequence known as the Shine-Dalgarno sequence.
Step 2: Role of the Shine-Dalgarno sequence
The Shine-Dalgarno sequence is a purine-rich region located about 6--10 nucleotides upstream of the start codon on mRNA. It base-pairs with a complementary sequence on the 3$^\prime$ end of the 16S rRNA of the small (30S) ribosomal subunit.
Step 3: Function of 16S rRNA in initiation
This base-pairing helps align the ribosome correctly with the start codon and is essential for the initiation of protein synthesis in prokaryotes. Therefore, the correct answer is: 16S rRNA.
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