Lac operon is

Options

A. repressible system
B. inducible system
C. five structural genes control it
D. controlled by regular gene

Answer

**Step-by-Step Text Solution:**

1. **Definition of Lac Operon**: The Lac operon is a genetic regulatory system found in E. coli and other bacteria that controls the metabolism of lactose. It serves as a model for understanding gene regulation.

2. **Structure of Lac Operon**: The Lac operon consists of several key components:
- **Promoter**: A sequence where RNA polymerase binds to initiate transcription.
- **Operator**: A sequence that acts as a regulatory switch, where a repressor can bind.
- **Structural Genes**: These include lacZ, lacY, and lacA, which code for enzymes that help in the metabolism of lactose.

3. **Function in Absence of Lactose**: When lactose is not present in the environment:
- A repressor molecule binds to the operator region.
- This binding blocks RNA polymerase from transcribing the structural genes.
- As a result, the enzymes necessary for lactose metabolism are not produced.

4. **Function in Presence of Lactose**: When lactose is present:
- Lactose molecules bind to the repressor, causing it to change shape and release from the operator.
- This allows RNA polymerase to access the promoter and transcribe the structural genes (lacZ, lacY, and lacA).
- Consequently, the enzymes are produced, enabling the metabolism of lactose.

5. **Conclusion**: The Lac operon is an example of an inducible system, meaning that its expression is normally repressed but can be activated in response to the presence of lactose.

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