The trp operon is an example of what type of operon?

The trp operon is an example of what type of operon?

• A. Inducible
• B. Repressible
• C. Constitutive
• D. Negative control

Answer: (B)

Repressible operons are biosynthetic pathways that are normally active but can be shut off when the end product accumulates. The trp operon fits this pattern because it encodes enzymes to make tryptophan. When tryptophan is scarce, the repressor is inactive and transcription proceeds. When tryptophan builds up, it binds to the repressor, activating it, and the repressor-tryptophan complex binds the operator to block RNA polymerase, halting transcription. This makes the trp operon a repressible system driven by its own end product. Inducible operons, like the lac operon, are turned on by inducers; constitutive means always on.

Repressible operons are biosynthetic pathways that are normally active but can be shut off when the end product accumulates. The trp operon fits this pattern because it encodes enzymes to make tryptophan. When tryptophan is scarce, the repressor is inactive and transcription proceeds. When tryptophan builds up, it binds to the repressor, activating it, and the repressor-tryptophan complex binds the operator to block RNA polymerase, halting transcription. This makes the trp operon a repressible system driven by its own end product. Inducible operons, like the lac operon, are turned on by inducers; constitutive means always on.