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.
(a) It is said that 'lac operon' has to be operational at a very low level in the bacterial cell all the time. Justify.
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Solution and Explanation
The lac operon is switched on only when lactose (through its isomer allolactose) acts as the inducer and binds the repressor.
Step 2: Why a low basal level is needed:
Lactose cannot reach the inducer stage on its own. Lactose has to enter the cell through permease and be converted by beta-galactosidase.
If the operon were totally silent, the cell would have no permease and no beta-galactosidase to start this process.
So a very low level of the operon must be active all the time. Then, when lactose appears, a little enters, forms the inducer and switches the whole operon on.
Final Answer:
A basal level of permease and beta-galactosidase is needed so that lactose can enter the cell and be changed into the inducer that turns the operon on.
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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.
(b) (i) 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.
(b) (ii) Why is the regulation of operon called negative regulation ?
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