Question

The Shine--Dalgarno sequence is located in:

• A. Promoter region
• B. 52 untranslated region of mRNA
• C. Coding sequence
• D. Terminator region

Hint:

Associate "Shine-Dalgarno" with "Prokaryotic Ribosome Binding" and remember it must be on the mRNA \textit{before} the start codon, hence the 5' UTR. The eukaryotic equivalent is the Kozak consensus sequence.

Answer 1

The Correct Option is B

The Shine-Dalgarno sequence is a critical feature found in bacterial mRNA and plays a key role in the initiation of protein synthesis. To understand why the correct answer is the "5' untranslated region of mRNA", let's delve into the specifics of bacterial mRNA structure and function.

1. Understanding the Shine-Dalgarno Sequence:

   The Shine-Dalgarno sequence is a ribosomal binding site in bacterial messenger RNA (mRNA). It is located around six to ten nucleotides upstream of the start codon (AUG) in the 5' untranslated region (5' UTR) of the mRNA.

2. Function of the Shine-Dalgarno Sequence:

   This sequence is complementary to a region on the 16S rRNA of the small ribosomal subunit. The base pairing between the Shine-Dalgarno sequence and 16S rRNA helps to align the ribosome on the mRNA, ensuring that translation starts at the correct AUG start codon.

3. Justification of the Correct and Incorrect Options:

   • Promoter region: This region is involved in the initiation of transcription, not translation, and is located upstream of the coding sequence in DNA, not mRNA.
   • 5' untranslated region of mRNA: This is the correct answer. The Shine-Dalgarno sequence resides here, providing a site for ribosome binding.
   • Coding sequence: This is the region of the mRNA that is translated into protein, located downstream of the Shine-Dalgarno sequence.
   • Terminator region: This region signals the end of transcription, not part of the translation initiation sequence.

From the above explanation, it is clear that the Shine-Dalgarno sequence is indeed located in the 5' untranslated region of mRNA, and this placement is key to its role in protein synthesis initiation in bacteria.