Question

Which of the following process is regulated by the Trp operon?

• A. Tryptophan synthesis
• B. Tryptophan breakdown
• C. Interconversion of tryptophan
• D. Formation of precursor for tryptophan synthesis

Hint:

Remember the difference:
*lac* operon is inducible and regulates catabolism (breakdown of lactose).
*trp* operon is repressible and regulates anabolism (synthesis of tryptophan).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The tryptophan (*trp*) operon in E. coli is a classic example of a repressible operon that regulates the biosynthetic pathway of an essential amino acid.
Detailed Explanation:
- The *trp* operon consists of five structural genes (*trpE*, *trpD*, *trpC*, *trpB*, and *trpA*) that encode the enzymes responsible for the anabolic biosynthesis (synthesis) of tryptophan from chorismate.
- This operon is regulated by a negative repressible system:
- When tryptophan levels in the cell are low, the inactive Trp repressor cannot bind to the operator, allowing RNA polymerase to transcribe the genes required to synthesize tryptophan.
- When tryptophan is abundant, it acts as a co-repressor, binding to the Trp repressor to activate it.
- The active repressor-co-repressor complex binds to the operator, blocking transcription and shutting down tryptophan synthesis to conserve cellular energy.
- It does not regulate the catabolism (breakdown) of tryptophan.

Step 2: Final Answer:
The *trp* operon regulates the synthesis of tryptophan, corresponding to option (A).