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.
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.
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 codes for enzymes that use lactose. The question asks why it is never fully off.
The repressor does not block the operator with perfect efficiency, so a little transcription always leaks through.
Step 2: Role of the basal enzymes:
The operon carries three structural genes: lac z (beta-galactosidase), lac y (permease) and lac a (transacetylase).
Even at a low level, a few molecules of permease and beta-galactosidase are present in the cell.
Permease lets the first lactose molecules enter the cell. Beta-galactosidase changes some lactose into allolactose, the inducer.
Step 3: Why this is needed:
Allolactose binds the repressor and switches the operon on.
If there were no basal level, no lactose could enter and no inducer could form. The cell could never sense lactose in its surroundings.
Final Answer:
A low, constant level of permease and beta-galactosidase lets lactose enter, form the inducer and switch the operon on when lactose appears.
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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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