Cistrons, that codes for a polypeptide, in an operon are called

Options

A. Regulator genes
B. Structural genes
C. Premoter genes
D. Operator genes

Answer

To solve the question, "Cistrons, that code for a polypeptide, in an operon are called," we need to analyze the options provided and understand the definitions of each type of gene mentioned.

### Step-by-Step Solution:

1. **Understanding the Term 'Cistron':**
- A cistron is an alternative term for a gene. It refers to a segment of DNA that encodes for a specific polypeptide or protein.

2. **Identifying the Types of Genes:**
- The options given are:
- Regulator genes
- Structural genes
- Promoter genes
- Operator genes

3. **Analyzing Each Option:**
- **Regulator Genes:**
- These genes are responsible for controlling the expression of one or more genes. They do not directly code for proteins but instead regulate the activity of structural genes.
- **Structural Genes:**
- These genes carry the coding sequences for proteins (polypeptides). They are responsible for the synthesis of proteins and determine the primary structure of a polypeptide chain.
- **Promoter Genes:**
- Promoters are regions of DNA that initiate transcription of a particular gene. They are not genes themselves but are essential for the regulation of gene expression.
- **Operator Genes:**
- Operators are segments of DNA that interact with regulatory proteins to control the transcription of adjacent structural genes. They do not code for polypeptides.

4. **Conclusion:**
- The correct answer to the question is **Structural Genes** because these are the cistrons that code for polypeptides in an operon.

### Final Answer:
Cistrons that code for a polypeptide in an operon are called **Structural Genes**.

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