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.
How are the structural genes activated in the lac operon in E. coli ?
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.
How are the structural genes activated in the lac operon in E. coli ?
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Solution and Explanation
The i gene makes a repressor protein. With no lactose, the repressor binds the operator and blocks RNA polymerase. The structural genes stay off.
Step 2: Arrival of lactose:
When lactose is present, a little of it is changed to allolactose. This acts as the inducer.
The inducer binds the repressor and changes its shape.
Step 3: Switching on:
The changed repressor can no longer hold the operator. The operator is free.
RNA polymerase binds the promoter and transcribes lac z, lac y and lac a together as one mRNA.
This mRNA is then translated into the three enzymes.
Final Answer:
Lactose (allolactose) inactivates the repressor, the operator is freed, and RNA polymerase transcribes the structural genes z, y and a.
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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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