Question

UT EID: D. 5 E. 6 13. For the E. coli strain containing the following alleles of the lac operon, expression of lacZ and lacY is inducible, constitutively on or permanently repressed. (erepressor; r cannot bind operator: osoperator, o cannot bind repressor, lac are LOF mutations) A. lacZ is inducible, lacY is constitutively on. B. lacZ is constitutively on, lacY is inducible. C. lacZ is permanently repressed, lacY is constitutively on. D. lacZ is constitutively on, lacY is permanently repressed. E. Both lacZ and lacY are constitutively on 14. For the E. coli strain containing the following alleles of the trp operon, indicate which trp genes fully" constitutive even in the presence of tryptophan. cannot bind operator; o-operator, o (R=repressor, R att=attenuator; att. deletes the attenuator, P=promoter, t pare LOF mutations) cannot bind repressor, A. trpE and trpD B. trpC and trpB C. None of them are fully constitutive. D. All four of them are fully constitutive. 15. How can tryptophan synthesis be blocked even in the absence of tryptophan? A. When you mutate the operator so Trp repressor cannot bind. B. When you mutate the Trp repressor so it cannot bind to the operator nttenuation cannot occur

Answer 1

13. The answer is B. LacZ gene is constitutively on and lacY is inducible.

The repressor can acts in both cis and transmode. so, the functioal repressor fo second operon acts on first operon also. So, the gene Y is inducible and as the second operon has constitutive operator, the repressor cannnot binds to operator so it expresses continously.

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