Question

In the trp operon could Tryptophan get synthesized if the bacterial DNA was mutated at the site of the Promoter sequences? In other words, if the Promoter couldn’t function normally would Tryptophan be synthesized? Would you get a different answer depending on whether or not there was Tryptophan present in the cell? Give a molecular explanation.

Answer 1

Ans: Trp operon is involved in anabolic process of producing tryptophan and tryptophan is acting as a repressor molecule for this operon that means if the cell have enough amount of tryptophan then this operon switches off and vice-versa. Now coming to the question if the bacterial DNA is mutated at the site of the promoter sequence and it causes RNA polymerase to not able to bind with the promoter sequence and this will stop the transcription initiation of the genes involved in the anabolic pathway of tryptophan production and so the production of tryptophan because if the genes are not able to express than the substrate will not be converted into tryptophan.

When the cell has enough amount of tryptophan then the trp bound to the repressor changing the repressor to its active site, this active repressor attaches to the operator, blocking RNA polymerase from binding to the promoter and preventing transcription of the operon. So the concentration of tryptophan is only linked with the activation of repressor and not with the promoter mutation so we will get same answer whether or not there was tryptophan present in the cell.