In trp operon, the corepressor is

Options

A. 1)tryptophan
B. 2)lactose
C. 3)`beta`-galactoside
D. 4)glucose

Answer

**Step-by-Step Solution:**

1. **Understanding the TRP Operon:**
- The TRP operon is a group of genes in bacteria that are involved in the biosynthesis of the amino acid tryptophan. It is a classic example of a repressible operon.

2. **Identifying the Role of Corepressor:**
- In the context of operons, a corepressor is a small molecule that binds to a repressor protein, enabling it to bind to the operator region of the operon. This binding prevents transcription of the genes involved.

3. **Analyzing the Options:**
- The options provided are:
- a) Tryptophan
- b) Lactose
- c) Beta-galactoside
- d) Glucose

4. **Evaluating Each Option:**
- **Option a: Tryptophan**
- Tryptophan acts as a corepressor in the TRP operon. When tryptophan levels are high, it binds to the repressor protein, activating it. The active repressor then binds to the operator, blocking RNA polymerase and preventing transcription.
- **Option b: Lactose**
- Lactose is primarily associated with the lac operon, where it acts as an inducer, not a corepressor. Therefore, this option is incorrect.
- **Option c: Beta-galactoside**
- Beta-galactoside is a product of lactose metabolism and is not involved in the TRP operon. This option is also incorrect.
- **Option d: Glucose**
- Glucose does not act as a corepressor in the TRP operon. In fact, the presence of glucose can inhibit the expression of the lac operon but is not relevant to the TRP operon. Thus, this option is incorrect.

5. **Conclusion:**
- The correct answer is **Option a: Tryptophan**, as it is the corepressor in the TRP operon.

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