Operon unit consists of

Options

A. regulator, operator and repressive gene
B. regulator, structural and operator gene
C. regulator, structural, operator and promotor gene
D. regulator, structural and promoter gene

Answer

### Step-by-Step Solution:

1. **Understanding the Operon Concept**: An operon is a functional unit of genomic DNA that contains a cluster of genes under the control of a single promoter. It is primarily found in prokaryotes.

2. **Components of an Operon**: The basic components of an operon include:
- **Regulatory Gene**: This gene produces a repressor or activator protein that regulates the transcription of the operon.
- **Promoter**: A DNA sequence where RNA polymerase binds to initiate transcription of the downstream genes.
- **Operator**: A segment of DNA that a repressor protein can bind to, blocking RNA polymerase from transcribing the genes.
- **Structural Genes**: These are the genes that are transcribed into mRNA and translated into proteins. They usually encode enzymes or proteins necessary for a specific metabolic pathway.

3. **Example of a Lac Operon**: The lac operon is a well-studied example of an operon in E. coli that is involved in the metabolism of lactose. It consists of:
- **One Promoter**: Where RNA polymerase binds.
- **One Operator**: Where the repressor protein can bind.
- **One Regulatory Gene**: Produces the repressor protein.
- **Three Structural Genes (lacZ, lacY, lacA)**: These genes code for enzymes that help in lactose metabolism (e.g., β-galactosidase, lactose permease, and transacetylase).

4. **Conclusion**: Therefore, an operon unit consists of a regulatory gene, a promoter, an operator, and one or more structural genes.

### Final Answer:
An operon unit consists of a regulatory gene, a promoter, an operator, and structural genes.

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