L48: The lac operon

• What is the lac operon primarily responsible for?

  Regulating lactose metabolism in E. coli
• What happens to the lac operon when glucose is present?

  It is not constitutively transcribed
• What is the effect of glucose on the use of other carbon sources in E. coli?

  1. coli uses glucose first, then others
• What is the term for the growth pattern when E. coli uses two carbon sources?

  Diauxic growth
• What occurs during the lag phase of diauxic growth?

  1. coli cannot grow until glucose runs out
• What are the minimal growth requirements for E. coli?

  Minimal medium with glucose and histidine
• What proteins do the lac genes encode?

  lacY, lacZ, lacA
• What does lacY encode?

  β-galactoside-permease
• What does lacZ encode?

  β-galactosidase
• What is the function of lacA?

  Transfers an acetyl group to galactosides
• Why is the lac operon normally turned OFF?

  To prevent wasting energy on rare sugars
• What happens when the operator is bound by the repressor?

  The operon is turned OFF
• What is the role of allolactose in the lac operon?

  It disables the repressor
• How is allolactose formed?

  By the action of β-galactosidase (LacZ)
• What occurs when allolactose binds to the repressor?

  The operon is turned ON
• What is the effect of glucose on cAMP production?

  Glucose inhibits cAMP production
• What is catabolite repression?

  Bacteria prefer glucose over other sugars
• What is the significance of the lac promoter in biotechnology?

  It can control the expression of other genes
• Why is the lac promoter a good choice for gene expression?

  It allows controlled expression without energy waste
• What is IPTG?

  A lactose analogue used for induction
• What happens when IPTG is added to E. coli?

  It induces expression of lac operon genes
• What are housekeeping genes?

  Genes required for basic cellular functions
• Why are not all genes constitutively expressed?

  Making RNA and protein is energy costly
• What happens when E. coli is grown in minimal medium?

  It must synthesize all nutrients from inorganic sources
• What are the key messages regarding the lac operon?

  • Operons are groups of genes regulated together.
  • The lac operon is normally repressed.
  • Presence of lactose leads to de-repression.
  • Catabolite repression means preference for glucose.
  • The lac promoter is widely used in biotechnology.
• How can you distinguish between different E. coli strains?

  • Use selective media for growth.
  • Identify temperature-sensitive mutants.
  • Observe growth patterns on different carbon sources.
• What are the conditions for all E. coli strains to grow?

  • Minimal medium plus glucose.
  • Temperature at 30°C (permissive).
  • Rich medium at 30°C for separate growth.
• What is the structure of operons in prokaryotes?

  • A group of genes under one promoter.
  • Common in prokaryotes for coordinated regulation.
  • Produces polycistronic mRNA encoding multiple proteins.
• What is the role of adenylate cyclase in the lac operon regulation?

  • Converts ATP to cAMP.
  • Inhibited by glucose.
  • cAMP is necessary for CAP binding and transcription enhancement.
• What happens during the lag phase of E. coli growth on lactose?

  • Genes are transcribed and translated.
  • Proteins are folded and prepared for function.
  • Induction effects are measured after a few minutes.
• What is the significance of the β-galactosidase enzyme in the lac operon?

  • Catalyzes the formation of allolactose.
  • Breaks down lactose into glucose and galactose.
  • Plays a role in the regulation of the lac operon.
• What is the relationship between glucose and lactose metabolism in E. coli?

  • E. coli prefers glucose over lactose.
  • Glucose presence inhibits lactose gene expression.
  • Lactose metabolism occurs only after glucose is depleted.
• What is the role of Catabolite Activator Protein (CAP) in the lac operon?

  • Enhances transcription when bound to cAMP.
  • Interacts with RNA polymerase for efficient transcription.
  • Essential for effective lac operon expression in low glucose.
• What is the impact of rich medium on E. coli gene expression?

  • Genes for amino acid synthesis are switched off.
  • Nutrients are readily available, reducing metabolic costs.
  • Allows for faster growth compared to minimal medium.