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
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 |
Related textbook solutions
Related questions
1. What is the term when the product of a biochemical pathway inhibits the activity of the first enzyme of a pathway?
| feedback inhibition. | ||
| activator inhibition. | ||
| diffusional regulation. | ||
| enzyme activation. |
2. Through control of gene expression, prokaryotes respond to changing __________ conditions.
| internal | ||
| protein | ||
| environmental | ||
| genetic |
3. A protein that negatively regulates transcription by binding to the operator is known as the
| operon | ||
| repressor | ||
| activator | ||
| inducer |
4. During attenutation, when tryptophan levels are high, the ________ stem-loop forms and transcription ________ the trpL gene.
| 1-2, ends just past | ||
| 3-4, ends just past | ||
| 1-2, continues beyond | ||
| 3-4, continues beyond |
5. The process of turning on the expression of a gene in response to a substance in the environment is called:
| constituation. | ||
| repression. | ||
| induction. | ||
| catabolism. |
6. What is a function of some specific transcription factors?
| to bind to the promoter region of the gene to facilitate the proper alignment of the RNA polymerase | ||
| to bind to the centromere to induce meiosis | ||
| to bind to enhancer regions to help regulate gene transcription | ||
| to bind to the operator to recruit sigma factor |
7. How does exposing an E.coli cell to glucose affect the regulation of the lac operon via CAP?
| cAMP binds to CAP and transcription is increased. | ||
| cAMP binds to CAP and transcription is decreased. | ||
| cAMP does not bind to CAP and transcription is increased. | ||
| cAMP does not bind to CAP and transcription is decreased. |
8. The lac repressor protein works when mutations in the repressor gene and structural genes are:
| in cis or in trans. | ||
| in trans only. | ||
| in cis only. | ||
| in both prokaryotes and eukaryotes. |
