Question

A mutation in the operator of the trp operon prevents the repressor to bind to the operator, even in the presence of tryptophan. What is true with respect to the bacteria carrying this mutation? Select one: a. The bacteria will transcribe the genes of the trp operon even when tryptophan is present in the environment b. Tryptophan would not be able to bind to the repressor protein c. Small amounts of tryptophan will be lethal for the bacteria d. The bacteria will die if it is not supplied with tryptophan from the environment e. tryptophan will bind to the CRP-CAMP complex to increase the transcription of the operon genes

Answer 1

The correct answer is option 'a' i.e. the bacteria will transcribe the genes of the trp operon even when tryptophan is present in the environment. Normally when tryptophan is present, it will act as co-repressor and help in activation of repressor. Repressor will bind to the operator present inside the promoter and thus turning trp operon off. Thus, there will be no transcription. But if the gene in operator is mutated in such a way that it prevent the binding of repressor, then the trp operon will always turned on and thus Transcription will continue whether tryptophan is present or not.

Please find the attached diagram for proper understanding.

thee of Trp 5) TOP DOFF Operon. T.R. B-TR 2) TtrpR zeto Tots at opeana I opern off No toonscription Apore pressor Top ja Co-gepoeder (PR<BTB) Repressor (Activel * If operator' get mutation and prevent prepressor from biroling, then I trp operon will always on and transription will continuer even in presence of tryptophan.