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 ââcuredââ by expressing wild-type trp repressor in them.
l) _____ These mutants can be ââcuredââ by transforming them with a wild-type trp operator.
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 ââcuredââ by expressing wild-type trp repressor in them.
l) _____ These mutants can be ââcuredââ by transforming them with a wild-type trp operator.
Related textbook solutions
Related questions
You are analyzing mutants in an Operon in an uncharacterized bacterial species using a method similar to what Jacob and Monod did to analyze the lac operon (see your text book Fig 14.7). This operon is induced in the presence of Sucrose to produce a sucrose metabolizing enzyme, the expression of which can be monitored using a reporter assay. A pink colored product is produced when an artificial substrate is added and the sucrose metabolizing enzyme is present. Like the ONPG assay, this assay is quantitative so the more enzyme, the darker the pink. In this operon, induction by sucrose is mediated by an Activator protein that when bound to its inducer sucrose, is able to bind to Operator A. The operon is also repressible by lactose. Repression by lactose is mediated by a Repressor protein that when bound to its co-repressor lactose, is able to bind to Operator B.
Based on this description, state whether the activator, the repressor, both, or neither would be bound to their respective operators under each set of conditions in wild type bacteria.
| No Lactose No Sucrose | Lactose No Sucrose | No Lactose Sucrose | Lactose Sucrose | |
| Wild Type |
A series of mutants is described below:
Activator Mutant A â Activator cannot bind to DNA
Activator Mutant B â Activator cannot bind to sucrose
Repressor Mutant A â Repressor cannot bind to DNA
Repressor Mutant B â Repressor cannot bind to lactose
Pink color was measured in wild type bacteria under the listed conditions. Based on the measurements in the wild type condition, state the amount of pink color that would be produced.
| -Lactose -Sucrose | +Lactose -Sucrose | -Lactose +Sucrose | +Lactose +Sucrose | |
| Wild Type | 0.030 | 0.030 | 1.891 | 0.124 |
| Activator Mutant A | ||||
| Activator Mutant B | ||||
| Repressor Mutant A | ||||
| Repressor Mutant B |
