The figure below shows the mechanism of transcription termination at the trp att
ID: 180238 • Letter: T
Question
The figure below shows the mechanism of transcription termination at the trp attenuator in wild-type E. coli cell. Select one of the following responses regarding the trp operon system
If you introduced mutations in region 1 to eliminate Trp codons from the leader peptide, what type of response would you expect from this mutant E. coli strain?
A- Transcription is terminated at the trp operon attenuator only at high concentration of Trp
B- Transcription is terminated at the trp operon attenuator only at low concentration of Trp
C- Transcription is terminated at the trp operon attenuator at both high and low concentrations of Trp
D- Transcription is not terminated at the trp operon attenuator at any concentration of Trp
a high tryptophan leader peptide coding region b low tryptophan leader peptide trp operon mRNA tryptophan codons C no protein synthesis Copyright 2004 Pearson Education, Inc., publishing as Benjamin CummingsExplanation / Answer
Important points to be consider:
* If trp is high in the medium, ribosome translates leader sequence, hence transcription termination occurs --------Tryptophan turned off
* If trp is low in the medium, ribosome stalls on the leader sequence, hence transcription termination does not occur because of trp regulated genes--------Tryptophan turned on
Mutants cannot be fully induced/repressed by the trptophan
If we introduce mutations in region 1 to eliminate Trp codons from the leader peptide in E.Coli strain then,
D- Transcription is not terminated at the trp operon attenuator at any concentration of Trp.