Repressible operon

Definition

A repressible operon is a cluster of genes controlled by a single promoter, which can be turned off by a repressor protein in response to specific environmental conditions. Typically, these operons regulate anabolic pathways and are inhibited when the end product is abundant.

5 Must Know Facts For Your Next Test

1. Repressible operons are usually involved in anabolic (biosynthetic) pathways.
2. The trp operon in E. coli is a classic example of a repressible operon.
3. When the end product (e.g., tryptophan) is abundant, it acts as a corepressor and binds to the repressor protein, activating it.
4. The activated repressor-corepressor complex binds to the operator region of the operon, blocking transcription.
5. In the absence of the end product, the repressor remains inactive, allowing gene transcription to proceed.

Review Questions

• What type of metabolic pathways do repressible operons typically regulate?
• How does the presence of an end product like tryptophan affect a repressible operon?
• What happens at the molecular level when an end product is absent in a cell with a repressible operon?

Related terms

Inducible Operon: A cluster of genes that are usually off but can be activated by an inducer molecule.

Corepressor: A small molecule that binds to a repressor protein, enabling it to turn off gene expression in a repressible operon.

Operator:

A segment of DNA within or near an operon's promoter that acts as a binding site for regulatory proteins like repressors.