You are analyzing mutants in an Operon in an uncharacterized bacterial species u
ID: 256774 • Letter: Y
Question
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 – Activator cannot bind to DNA
Activator Mutant B – Activator cannot bind to sucrose
Repressor Mutant A – Repressor cannot bind to DNA
Repressor Mutant B – 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
No Lactose
No Sucrose
Lactose
No Sucrose
No Lactose Sucrose
Lactose
Sucrose
Wild Type
Explanation / Answer
No lactose
No sucrose
Lactose
No sucrose
No lactose
Sucrose
Lactose
sucrose
Wild type
Neither
Repressor
Activator
both
-lactose
-sucrose
+lactose
-sucrose
-lactose
+sucrose
+lactose
+sucrose
Wild type
0.030
0.030
1.891
0.124
Activator mutant A
0.030
0.030
0.030
0.030
Activator mutant B
0.030
0.030
0.030
0.030
Repressor mutant A
0.030
0.030
1.891
1.891
Repressor mutant B
0.030
0.030
1.891
1.891
No lactose
No sucrose
Lactose
No sucrose
No lactose
Sucrose
Lactose
sucrose
Wild type
Neither
Repressor
Activator
both
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