Question

30. How many different secondary structures (loops) can be formed from the mRNA of the leader region (trpL)?

A) one

B) two

C) three

D) four

E) five

Answer 1

Answer: Option C is correct.
Explanation:
Trp operon is a biosynthetic operon. It is an example of repressible negative regulation. It contains five structural genes which are required for the biosynthesis of tryptophan.
When Trp is present, an anti-terminator sequence is formed which prevents RNA polymerase from transcribing the operon.
When Trp is absent, RNA polymerase transcribes the operon.

The leader sequence of Trp operon contains four sequences that can sense and regulate the transcription of the operon (Attenuation). It contains four specific regions which can pair with others to form three distinct secondary (hairpin loop) structures due to sequence complementarity. They are,
i. 1&2
2. 2&3
3. 3&4

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