Read the following passage and answer the questions that follow :
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.
(ii) Why is the regulation of operon called negative regulation ?
Read the following passage and answer the questions that follow :
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.
(ii) Why is the regulation of operon called negative regulation ?
Show Hint
Solution and Explanation
In negative regulation, a repressor protein switches the genes off. Genes work only when something removes the repressor.
Step 2: Apply it to the lac operon:
The repressor binds the operator and stops transcription of the structural genes.
Because the control is exerted by a protein that blocks transcription, the regulation is called negative.
Final Answer:
The repressor binds the operator and prevents transcription, so the operon is controlled by switching it off. This is negative regulation.
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\[ \begin{array}{|c|c|} \hline \textbf{A: Gene} & \textbf{B: Products} \\ \hline \text{a. ‘i’ gene} & \text{(i) β-galactosidase} \\ \text{b. ‘z’ gene} & \text{(ii) lac permease} \\ \text{c. ‘a’ gene} & \text{(iii) repressor} \\ \text{d. ‘y’ gene} & \text{(iv) transacetylase} \\ \hline \end{array} \] Select the correct option:
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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.
(a) It is said that 'lac operon' has to be operational at a very low level in the bacterial cell all the time. Justify.
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.
(b) (i) How are the structural genes activated in the lac operon in E. coli ?
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