Operons

DNA Structure and Function

• Types of Cells: Eukaryotic vs. Prokaryotic

  • Eukaryotic cells: Individual genes transcribed and translated.

  • Prokaryotic cells: Groups of genes (operons) transcribed and translated together.

Operons

• Definition: A group of genes regulated together in prokaryotic cells.

• Lactose Operon: An example of an inducible operon.

  • Components:

    • Regulator Gene: Codes for the repressor protein (downstream of operon).

    • Promoter Gene: Binding site for RNA polymerase.

    • Operator Gene: Binding site for repressor protein.

    • Structural Genes: Three genes coding for enzymes needed to break down lactose.

Inducible Operon (Lactose Operon)

• Function: Typically off unless substrate (lactose) is available.

  • When lactose is present, it binds to the repressor, removing it from the operator.

  • RNA polymerase can then bind to promoter, allowing transcription and translation.

  • When lactose is depleted, the repressor binds back to the operator, halting the process.

Repressible Operon

• Definition: Another operon type with similar components to inducible operons but functions differently.

  • Function: Usually 'on', actively transcribing until its product accumulates (e.g., arginine).

  • Accumulation of end product binds the repressor, which then blocks transcription by binding to the operator.

Summary of Efficiency

• Both operons enhance metabolic efficiency by regulating enzyme production based on substrate availability or product accumulation.