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What would happen to gene regulation in the lac operon in
Escherichia coli if the following mutations were made? Support your answer.

a. A nonsense mutation in LacI

b. A mutation decreasing the activity of acetylcholine esterase.

c. Swapping out the repressor sequence for the repressor in the tryptophan

operon.

d. A mutation that changes a CGG to an AGG in the CAP protein.

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Keith Leannon
Keith LeannonLv2
28 Sep 2019

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Related questions

1. Predict the consequences of the following alterations to genes involved in operon regulation.

A. A mutation in the trpR gene that produces a protein that cannot bind to the tryptophan operon DNA sequence.

B. A mutation in the CAP gene that prevents its protein from binding to cAMP.

C. A mutation in the I region of the ara operon that prevents it from binding to the araC protein

D. A mutation in the I gene of the lac operon that produces a repressor that is unable to bind to the inducer.

*There was no additional information provided for this assignment*

Consider E. coli cells with thefollowing mutations. What effect would each mutation have on theexpression of the lac operon (assuming no glucose is present)? Makesure to justify your answer.

(A) A mutant lac operator that cannot bind repressor (1pt)

(B) A mutant lac repressor that cannot bind to allolactose(1pt)

(C) A mutant lac promoter that cannot bind CAP-cAMPcomplex(1pt)

Just to clarify, A, B, and C are situations, and the question isasking what would happen in each situation. Thanks

The following test deals with the regulation of the trp operon of Escherichia coli. Two mutants of this operon are described: in mutant A, the operator region of the operon carries a point mutation so that it is unable to carry out its function; mutant B expresses a trp repressor protein unable to bind tryptophan. Review the principle of the regulation of this operon and then solve the following questions related to the behavior of the mutant cells using the options below.

A: Mutant A B: Mutant B C: Both of them D: Neither of them

a) _____ In the presence of tryptophan these cells behave like wild-type cells. b) _____ In the absence of tryptophan these cells behave like wild-type cells. c) _____ These cells are able to synthesize tryptophan.
d) _____ These cells are able to break down tryptophan.

e) _____ Tryptophan is able to act as an inducer in these cells.
f) _____ Tryptophan is able to act as a corepressor in these cells.
g) _____ The structural genes of the trp operon can be transcribed in these cells.
h) _____ In the presence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
i) _____ In the absence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
j) _____ These cells die if tryptophan is omitted from their medium.
k) _____ These mutants can be ‘‘cured’’ by expressing wild-type trp repressor in them.
l) _____ These mutants can be ‘‘cured’’ by transforming them with a wild-type trp operator.

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