Who were the first to elucidate a transcriptionally regulated system?

Options

A. Fracois Jacob and Jacque Monod
B. Alfred Hershey and Martha Chase
C. Oswald Avery and MacLeod
D. Severo Ochoa and Nirenberg

Answer

To answer the question "Who were the first to elucidate a transcriptionally regulated system?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the individuals who first explained a system that regulates the transcription of DNA into RNA. This is a fundamental concept in molecular biology.

2. **Define Transcriptionally Regulated System**: A transcriptionally regulated system refers to the mechanisms by which cells control the expression of genes at the transcription stage, converting DNA into RNA.

3. **Identify Key Scientists and Their Contributions**:
- **Francois Jacob and Jacques Monod**: They are known for their work on the LAC operon in E. coli, which is a classic example of a transcriptionally regulated system. They elucidated how the presence or absence of lactose affects the expression of genes involved in its metabolism.
- **Alfred Hershey and Martha Chase**: They demonstrated that DNA is the genetic material by showing how bacteriophages infect bacteria, but they did not focus on transcription regulation.
- **Oswald Avery and colleagues**: They showed that DNA can transform the properties of a cell, but again, this does not directly relate to transcription regulation.
- **Severo Ochoa and Marshall Nirenberg**: They contributed to understanding the genetic code and protein synthesis, but they did not specifically elucidate transcription regulation.

4. **Conclusion**: Based on the contributions of these scientists, it is clear that Francois Jacob and Jacques Monod were the first to elucidate a transcriptionally regulated system through their work on the LAC operon.

### Final Answer:
Francois Jacob and Jacques Monod were the first to elucidate a transcriptionally regulated system.

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