Prokaryotic Gene Regulation

Key Notes

What You Will Learn

• How transcription is regulated in prokaryotes

• The role of operons in gene regulation

Prokaryotic Gene Regulation

• Prokaryotic transcription regulation is simpler than in eukaryotes

• Gene expression is controlled to conserve energy and resources

• Operons play a key role in transcription regulation

What is an Operon?

• An operon is a DNA region containing:

  • Genes encoding proteins for a specific function

  • A promoter where RNA polymerase binds

  • An operator, a DNA segment where regulatory proteins bind to control transcription

The Lac Operon (E. coli Example)

• The lac operon controls lactose metabolism in bacteria

• Includes three genes: lacZ, lacY, and lacA, which encode enzymes for lactose digestion

• Regulation based on lactose presence:

  • Lactose absent → A repressor protein binds to the operator, blocking RNA polymerase → No transcription

  • Lactose present → The repressor does not bind, RNA polymerase transcribes the genes → Enzymes digest lactose

Why Regulate Gene Expression?

• Saves energy and materials by producing proteins only when needed

• Ensures efficient resource utilization

Summary

• Prokaryotic gene regulation mainly involves operons

• Lac operon regulation depends on lactose presence

• The operator controls transcription by binding regulatory proteins

Review Questions

1. What is an operon?

2. Why might it be beneficial to express genes only when they are needed?

3. What is the role of an operon's operator?

4. What happens to the lac operon in the absence of lactose?

5. Draw a diagram to show how the lac operon is regulated.