Question

The mRNA that is transcribed from the trpL region can alternately fold to form three possible stem-loop structures. Different stem-loop structures have varying effects on transcription.

Which stem-loop structure is responsible for terminating transcription?


A. the 1-2 stem loop
B. the 2-3 stem loop
C. the 3-4 stem loop

Answer 1

The 3-4 stem loop is responsible for terminating transcription in the trp operon due to the process of attenuation.

Step-by-step explanation:

The stem-loop structure responsible for terminating transcription in the trp operon regulatory region is the 3-4 stem loop. This terminator loop forms when tryptophan is abundant, leading to the conclusion of the transcription process. When this loop is formed, transcription terminates, and the RNA polymerase releases from the mRNA. When tryptophan levels are low, the antiterminator loop (formed between regions 2 and 3) allows transcription to continue, enabling the synthesis of proteins that will ultimately synthesize tryptophan. This mechanism is an example of attenuation, which is a form of gene regulation that utilizes secondary structures in the mRNA to control transcription.