Question:
Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.
(c) Why is lac operon said to be a transcriptionally regulated system ?
Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.
(c) Why is lac operon said to be a transcriptionally regulated system ?
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Repressor, operator and inducer control mRNA synthesis, so regulation is at the transcription level.
Updated On: Oct 22, 2026
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Solution and Explanation
Step 1: Find the step that is controlled:
Gene expression has two main stages: transcription (DNA to mRNA) and translation (mRNA to protein).
Step 2: Where the lac operon is controlled:
The repressor and the inducer decide whether RNA polymerase can transcribe the lac genes. If the operator is blocked, no mRNA is made.
If lactose is present, the repressor is inactivated and mRNA is made.
Step 3: Conclusion:
The control acts on the synthesis of mRNA, that is, at the level of transcription. So the operon is a transcriptionally regulated system.
Final Answer:
The switching on and off of the lac genes happens at the level of mRNA synthesis (transcription), by the repressor, operator and inducer.
Gene expression has two main stages: transcription (DNA to mRNA) and translation (mRNA to protein).
Step 2: Where the lac operon is controlled:
The repressor and the inducer decide whether RNA polymerase can transcribe the lac genes. If the operator is blocked, no mRNA is made.
If lactose is present, the repressor is inactivated and mRNA is made.
Step 3: Conclusion:
The control acts on the synthesis of mRNA, that is, at the level of transcription. So the operon is a transcriptionally regulated system.
Final Answer:
The switching on and off of the lac genes happens at the level of mRNA synthesis (transcription), by the repressor, operator and inducer.
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