Overview of the Trp Operon in E. coli

Structure of the Trp Operon

• Contains five structural genes:
  • trpE
  • trpD
  • trpC
  • trpB
  • trpA
• These genes encode enzymes essential for tryptophan synthesis.
• Tryptophan is crucial for protein synthesis in E. coli.

Operon Components

• Promoter and Operator: Shared by the five structural genes.
• Regulatory Gene (trpR): Located upstream of the operon.
  • Encodes an inactive repressor.

Function of the Trp Operon

Derepressed State

• Inactive Repressor:
  • Cannot bind to the operator.
  • Allows RNA polymerase to bind to the promoter and transcribe structural genes.
• Result: Production of enzymes for tryptophan synthesis.

Repressed State

• Role of Tryptophan:
  • Acts as a co-repressor.
  • Binds to the inactive repressor, activating it.
• Activated Repressor:
  • Binds to the operator.
  • Prevents RNA polymerase from transcribing genes.
• Result: Limits transcription and conserves energy when tryptophan is abundant.

Key Concepts

• Repressible Operon:
  • Genes are naturally expressed.
  • Excess environmental tryptophan is needed to repress gene expression.

Summary

• Low Tryptophan:
  • Repressor is inactive.
  • Genes are transcribed and translated, producing tryptophan.
• High Tryptophan:
  • Repressor is activated.
  • Transcription of trp structural genes is limited, preventing additional tryptophan production.

Additional Resources

• Review operon basics by checking out resources on general operon understanding.
• Explore more on different operons, such as the lac operon.