Q. In the absence of lactose, what is the state of the lac operon?
A.
Fully active
B.
Partially active
C.
Inactive
D.
Overactive
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Solution
In the absence of lactose, the lac operon is inactive because the lac repressor binds to the operator, blocking transcription.
Correct Answer:
C
— Inactive
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Q. What happens when lactose is present in the environment of E. coli?
A.
The lac repressor binds to the operator
B.
Transcription of the lac operon is inhibited
C.
The lac repressor is inactivated
D.
cAMP levels decrease
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Solution
When lactose is present, it binds to the lac repressor, causing a conformational change that inactivates the repressor and allows transcription of the lac operon.
Correct Answer:
C
— The lac repressor is inactivated
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Q. What is the effect of high glucose levels on the lac operon?
A.
Increased transcription
B.
Decreased transcription
C.
No effect
D.
Inhibition of repressor
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Solution
High glucose levels lead to low cAMP levels, which decreases the transcription of the lac operon.
Correct Answer:
B
— Decreased transcription
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Q. What is the primary function of the lac operon in E. coli?
A.
To regulate amino acid synthesis
B.
To control lactose metabolism
C.
To enhance DNA replication
D.
To promote cell division
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Solution
The lac operon regulates the metabolism of lactose in E. coli by controlling the expression of genes required for lactose uptake and breakdown.
Correct Answer:
B
— To control lactose metabolism
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Q. What is the role of lactose permease in the lac operon?
A.
To synthesize lactose
B.
To transport lactose into the cell
C.
To degrade lactose
D.
To inhibit the repressor
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Solution
Lactose permease is a membrane protein that facilitates the transport of lactose into the E. coli cell.
Correct Answer:
B
— To transport lactose into the cell
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Q. What role does cAMP play in the regulation of the lac operon?
A.
It inhibits transcription
B.
It enhances RNA polymerase binding
C.
It degrades mRNA
D.
It activates the repressor
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Solution
cAMP enhances the binding of RNA polymerase to the promoter of the lac operon, facilitating transcription when glucose levels are low.
Correct Answer:
B
— It enhances RNA polymerase binding
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Q. What type of regulation is exemplified by the lac operon?
A.
Positive regulation
B.
Negative regulation
C.
Feedback inhibition
D.
Transcriptional activation
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Solution
The lac operon is an example of negative regulation, where the binding of the repressor to the operator inhibits transcription.
Correct Answer:
B
— Negative regulation
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Q. Which enzyme is responsible for the hydrolysis of lactose in E. coli?
A.
Lactase
B.
Beta-galactosidase
C.
Lactose permease
D.
Galactosidase
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Solution
Beta-galactosidase is the enzyme that hydrolyzes lactose into glucose and galactose in E. coli.
Correct Answer:
B
— Beta-galactosidase
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Q. Which of the following is NOT a component of the lac operon?
A.
Promoter
B.
Operator
C.
Repressor
D.
Enhancer
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Solution
The lac operon consists of a promoter, operator, and structural genes, but does not include an enhancer.
Correct Answer:
D
— Enhancer
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Q. Which protein binds to the operator region of the lac operon?
A.
RNA polymerase
B.
Lac repressor
C.
cAMP receptor protein
D.
Beta-galactosidase
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Solution
The lac repressor binds to the operator region of the lac operon, preventing transcription of downstream genes when lactose is absent.
Correct Answer:
B
— Lac repressor
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