Question

Your lab is studying gene expression of the tryptophan operon in the bacterium E. coli. In order to facilitate this study, you have cloned the Trp-operon, excised the five coding genes (TrpA, B, C, D, and E), and replaced them with a copy of the reporter gene GFP (green fluorescent protein). The resulting recombinant DNA was inserted into an F' plasmid, and used to transform a number of different strains of E. coli. For each of the scenarios listed below, predict what the bacterial colonies would look like, and explain why you would obtain these results.

a. A "wild type" strain of E. coli, transformed by the F' Trp/GFP reporter plasmid, is plated out on a selective medium lacking tryptophan.

b. A "wild type" strain of E. coli, transformed by the F' Trp/GFP reporter plasmid, is plated out on tryptic soy medium.

c. A trpR mutant strain of E. coli, transformed by the F' Trp/GFP reporter plasmid, is plated out on tryptic soy medium.

Answer 1

a. in this case, when strains are plated on tryptophan lackig medium, bacteria can not grown because they required tryptophane to activate transciption process. lack of trptophane leads to activation of repressor which stops the activity of RNA polymerase. transciption is blocked and no proteing is formed from gene hence GFP is not expressed.

b. in this case strains contain GFP can grow on tryptic soya medium. the tryptic soya medium is a tryptophane reach media for bacteria growth containing trp operon. transciption leads to form a protein hence GFP preotein in expressed and colony containing this GFP protein, grown on media.

c. trpR is a gene codes for repressor molecules. repressor molecules generally stops the transciption by stoping the activity of RNA polymerase. though the media is rich with trypophan (tryptic soya medium), GFP can not transcribed and protein is not formed. hence colonies containing trp/ GFP can not grown.