Gene regulation - lac operon

• Operon = a section of DNA that contains a group of genes transcribed together
• Structural gene = codes for lac enzymes
• Regulatory gene = produces repressor proteins that control the expression of a structural gene, by binding to operator region
• RNA polymerase = binds to promoter region
• Repressor protein = binds to operator region
• Why are genes switched on in bacteria that is moved to a medium that has lactose?

  • The repressor protein is binded to the operator region of the lac operon
  • Lactose binds to the repressor protein
  • This causes it to change shape + move away
  • As its no longer binded to operator region
  • Now, RNA polymerase binds to the promoter region
  • At this point the gene is switched on
  • mRNA is transcribed
  • mRNA is translated into the protein
  • enzymes e.g. lactase produced - break down lactose