In tryptophan operon, the tryptophan acts as

Options

A. corepressor
B. promoter
C. apo-repressor
D. operator

Answer

To answer the question about the role of tryptophan in the tryptophan operon, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Tryptophan Operon**:
- The tryptophan operon is a classic example of a repressible operon, which is a type of genetic regulatory system.
- It is involved in the synthesis of the amino acid tryptophan.

2. **Components of the Operon**:
- The operon consists of several key components:
- **Regulatory Gene (R)**: Produces a molecule known as the aporepressor.
- **Promoter (P)**: The site where RNA polymerase binds to initiate transcription.
- **Operator (O)**: The segment where the repressor binds to block transcription.
- **Structural Genes**: These genes (E, D, C, B, A) encode the enzymes necessary for tryptophan synthesis.

3. **Role of Tryptophan**:
- Tryptophan acts as a **co-repressor** in this operon system.
- When tryptophan levels are high, it binds to the aporepressor, forming a complex that can effectively bind to the operator.

4. **Mechanism of Action**:
- The binding of the tryptophan-aporepressor complex to the operator prevents RNA polymerase from transcribing the structural genes.
- This inhibition stops the synthesis of tryptophan, thus regulating its own production.

5. **Feedback Mechanism**:
- As tryptophan is consumed and its levels decrease, the aporepressor is no longer activated by tryptophan.
- This allows the operator to be unblocked, and transcription of the structural genes resumes, leading to the production of more tryptophan.

6. **Conclusion**:
- Therefore, in the context of the question, tryptophan acts as a **co-repressor** in the tryptophan operon.

### Final Answer:
Tryptophan acts as a **co-repressor** in the tryptophan operon.

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