LacOp

I. Using the above diagram and your knowledge of the lac operon, answer the following questions.

Lac Operon Structures/Components

1. The lac repressor binds to what site within the lac operon?

Promoter
Operator
Regulator
Structural Genes

2. Which of the following does NOT encode for a protein that is directly involved in metabolizing lactose?

lacZ
lacY
lacI
lacA

3. The lac repressor is inactivated by binding to _________ which is derived from ___________?

Allolactose, lactose
β-galactosidase, galactose
Transcription factors, glucose
RNA Polymerase, lactose

4. Which of the following encode a protein that plays a direct role inregulating the expression of the Lac operon?

lacI
lacP
lacO
lacZ

Predicting Outcomes

5. Is mRNA transcribed from the lac operon when lactose is present AND glucose is not present in the cell? Why or why not?

No, because the inducer is not present
Yes, because the inducer is present
No, because the inducer is present
Yes, because the inducer is not present

6. Is the lac repressor active in the absence of lactose within the cell? Why or why not?

Yes, the repressor is active because the inducer is not present.
Yes, the repressor is only active in the presence of lactose
No, the repressor is not active because the inducer is not present.
None of the above

II. For the following questions use the information provided in each question, the diagram, and your knowledge of the lac operon to give your best answer.

Mutations

7. Predict the phenotype of an E. coli with a lacI- mutation in an otherwise normal genome.

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.

8. . If a second, normal (wild-type), copy of the lacI gene is inserted into a cell with a lacImutation what will the phenotype of this partial diploid be?

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.

9. Predict the phenotype of an E. coli cell with a lacIS, “super repressor,” mutation in an otherwise normal genome.

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.

10. If a normal copy of the lacIgene were inserted into a cell with the lacIS mutation what would the phenotype of this partial diploid be?

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.

11. An operator mutation,lacOC, prevents the operator from being bound by the repressor. Predict the phenotype of an E. coli cell with this mutation

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.

12. Using your knowledge of the lac operon, predict the phenotype of a cell that exhibits a loss of function mutation in the promoter.

The lac genes would only be transcribed in the absence of lactose.
The lac genes would only be transcribed in the presence of lactose.
The lac genes would be transcribed continuously.
The lac genes would never be transcribed efficiently.