A gene that takes part in synthesis of polypeptide is

Options

A. Promotor gene
B. Structural gene
C. Regulator gene
D. Operator gene

Answer

To solve the question "A gene that takes part in the synthesis of polypeptide is", we need to analyze the options provided and understand the role of each type of gene mentioned.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a type of gene that is directly involved in the synthesis of polypeptides. Polypeptides are chains of amino acids that make up proteins, and their synthesis is a crucial part of gene expression.

2. **Analyzing Option A - Promoter Gene**:
- A promoter gene is a region of DNA that initiates transcription of a particular gene. It serves as a binding site for RNA polymerase and is crucial for the transcription process.
- However, it does not directly code for polypeptides; it merely facilitates the process of transcription.
- **Conclusion**: Option A is incorrect.

3. **Analyzing Option B - Structural Gene**:
- Structural genes are those that code for proteins, including polypeptides. They contain the information needed to produce a specific polypeptide chain.
- Since the question specifically asks for a gene involved in the synthesis of polypeptides, structural genes are indeed responsible for this process.
- **Conclusion**: Option B is correct.

4. **Analyzing Option C - Regulator Gene**:
- Regulator genes are involved in the regulation of gene expression. They produce proteins that can enhance or inhibit the expression of other genes, but they do not directly code for polypeptides themselves.
- **Conclusion**: Option C is incorrect.

5. **Analyzing Option D - Operator Gene**:
- Operator genes are segments of DNA that a repressor protein can bind to, thus regulating the transcription of adjacent genes. They play a role in controlling gene expression but do not code for polypeptides.
- **Conclusion**: Option D is incorrect.

6. **Final Answer**: After analyzing all the options, the gene that takes part in the synthesis of polypeptides is **Option B - Structural Gene**.