A mutant E. coli strain is isolated that shows inappropriate regulation of the t
ID: 60324 • Letter: A
Question
A mutant E. coli strain is isolated that shows inappropriate regulation of the trp operon. The relative expression of the operon in low or high tryptophan conditions is given in the table below. Expression is also quantified in a merozygote strain that has an F! plasmid with a wild type copy of the trp operon (only the operon itself, not additional DNA sequences).
A) What regulatory mechanism(s) is mostly not functioning properly in the mutant
B) Explain what gene or DNA sequence is likely mutated, and whether the mutation is leading to a loss of function or a new/increased function
E. coli strain T Tryptophan Level Relative Mutant Mutant Merozygote Merozygote Expression 100 10 200 12 Low High Low HighExplanation / Answer
a. In regulation, we see two trp molecules binding to a repressor molecule and then binding to the operator of the trp operon. This prevents the expression of the operon. This happens when there is plenty of trp. But we see from the above data that the mutant produces only half of what is needed. The negative feedback regulatory mechanism is affected.
b. so we can say that the repressor gene is mutated. IT produces repressor which binds to the operator at medium concentrations of trp. This leads to decrease in function.
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