Describe lac-operon with diagram.
Solution and Explanation
Introduction
The lac operon is a set of genes in E. coli that is involved in the metabolism of lactose. It is one of the most studied examples of gene regulation in prokaryotes. The operon consists of three structural genes, a promoter, an operator, and a regulator gene. The lac operon is an example of inducible gene expression.
Components of the Lac Operon
- Structural Genes:
- lacZ: Encodes the enzyme β-galactosidase, which breaks down lactose into glucose and galactose.
- lacY: Encodes permease, a membrane protein that facilitates the entry of lactose into the cell.
- lacA: Encodes transacetylase, an enzyme involved in the detoxification of by-products during lactose metabolism.
- Regulatory Region:
- Promoter (P): The site where RNA polymerase binds to initiate transcription.
- Operator (O): The region where the lac repressor protein binds to prevent transcription.
- Regulator gene (I): Codes for the lac repressor, which binds to the operator in the absence of lactose to inhibit transcription.
- Inducer (Allolactose): Allolactose, a metabolite of lactose, is the inducer that inactivates the lac repressor by binding to it. This allows RNA polymerase to bind to the promoter and transcribe the lac genes.
Regulation of the Lac Operon
The lac operon is under negative control. In the absence of lactose, the repressor protein binds to the operator, preventing the transcription of the lac genes. When lactose is present, allolactose binds to the repressor, causing a conformational change that prevents the repressor from binding to the operator. This allows RNA polymerase to transcribe the operon, enabling the metabolism of lactose.
Diagram
Below is a diagram of the lac operon showing its components and the regulatory mechanism:
Conclusion
The lac operon is a well-understood model of gene regulation that exemplifies how bacteria can regulate gene expression in response to environmental changes. It allows E. coli to efficiently metabolize lactose only when it is available, conserving energy by avoiding unnecessary production of enzymes when lactose is absent.
Final Answer
Lac operon consists of genes lacZ, lacY, and lacA, with a promoter, operator, and repressor system for gene regulation.
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