In lac operon the lac mRNA

Options

A. Has several initial and termination codons
B. Forms four different enzyme
C. Is not transcribed in the presence of lactose
D. Is involved in an anabolic reaction

Answer

**Step-by-Step Solution:**

1. **Understanding the Lac Operon:**
The lac operon is a genetic system found in prokaryotes (like E. coli) that is responsible for the metabolism of lactose. It contains genes that code for enzymes necessary for the breakdown of lactose into glucose and galactose.

2. **Identifying the Components:**
The lac operon consists of three structural genes:
- **Z gene:** Codes for beta-galactosidase, which breaks down lactose.
- **Y gene:** Codes for permease, which facilitates the entry of lactose into the cell.
- **A gene:** Codes for transacetylase, which is involved in the transacetylation process.

3. **Function of the Lac mRNA:**
The lac mRNA is produced when the operon is activated. This occurs in the presence of lactose, which acts as an inducer. When lactose is present, it binds to the repressor protein, inactivating it. This allows RNA polymerase to transcribe the lac operon genes into mRNA.

4. **Analyzing the Options:**
- **Option 1:** States that lac mRNA is polycistronic. This is correct because it can code for multiple proteins (the three enzymes mentioned).
- **Option 2:** Suggests that lac mRNA is not transcribed in the presence of lactose. This is incorrect; lactose induces transcription.
- **Option 3:** Claims that it forms four different enzymes. This is incorrect; it forms three enzymes.
- **Option 4:** States that it is an anabolic reaction. This is incorrect; the lac operon is involved in catabolic processes.

5. **Conclusion:**
The correct answer is that the lac mRNA is polycistronic, as it codes for multiple enzymes necessary for lactose metabolism.

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