The trp operon in E. coli is similar to the lac operon. trpR encodes a repressor
ID: 52200 • Letter: T
Question
The trp operon in E. coli is similar to the lac operon. trpR encodes a repressor, trpO is the operator sequence, and trpA encodes the first enzyme in tryptophan biosynthesis. The regulation is different in this way, however: in the trp system, the repressor must bind to tryptophan before it can bind to the operator and repress transcription. A trpR-mutant is not able to bind tryptophan. A trpO- mutant cannot be bound by the repressor, and a trpA- mutant produces an inactive enzyme. Based on these data complete the following table.
Use a (+) to indicate activity and a (-) to indicate inactivity (-) of the trpA gene.
Genotype
No tryptophan
Tryptophan
R+O+A+
R-O+A-/R+O-A+
R+O-A+/R+O+A-
Genotype
No tryptophan
Tryptophan
R+O+A+
R-O+A-/R+O-A+
R+O-A+/R+O+A-
Explanation / Answer
Genotype
No tryptophan
Tryptophan
R+O+A+
+
-
R-O+A-/R+O-A+
+
+
R+O-A+/R+O+A-
-
-
Genotype
No tryptophan
Tryptophan
R+O+A+
+
-
R-O+A-/R+O-A+
+
+
R+O-A+/R+O+A-
-
-
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