Gene Expression and Transcriptional Regulation

Overview

• Gene expression can be transcriptionally regulated, which is essential in both eukaryotic and prokaryotic organisms.
• Transcriptional regulation was notably studied by Jacob, Mano, and Pari, focusing on the fermentation of lactose in Escherichia coli.

Lac Operon System

• Lac Operon: A classical model for studying transcriptional regulation.

Components of the Lac Operon

• Lac Z Gene: Codes for enzyme beta-galactosidase.
• Lac Y Gene: Codes for lactose permease.
• Lac A Gene: Codes for enzyme galactoside transacetylase.
• Lac P Region: Promoter region needed for transcription of Lac Z, Lac Y, and Lac A genes as a single polycistronic mRNA.
• Lac O Region: Operator site involved in transcriptional regulation.

Regulatory Mechanism

• Lac I Regulatory Gene: Codes for mRNA that produces the Lac repressor protein.
  • Lac Repressor:
    • In absence of lactose, it is active and binds to the Lac operator.
    • Prevents RNA polymerase from transcribing Lac operon genes.

Induction Process

• When lactose is present:
  • Converted to allolactose by beta-galactosidase.
  • Allolactose binds to Lac repressor, causing a conformational change.
  • Inactive Lac repressor cannot bind to the operator.
  • RNA polymerase binds to the promoter, transcribing a polycistronic mRNA for Lac Z, Lac Y, and Lac A genes.

Result of Induction

• Production of:
  • Beta-galactosidase
  • Lactose permease
  • Galactoside transacetylase
• Enables efficient lactose transport and metabolism in the cell.

Significance

• Lac Operon: Demonstrates how bacteria can respond to environmental changes via gene expression regulation.