Lecture Notes

Canvas Updates and Group Assignments

• Canvas updates may cause confusion with group assignments.
• Groups for short essays are labeled as "Groups" on the Canvas page, not listed in discussions anymore.
• Students should check under "People" and "Groups" to find their group assignments.
• Use Piazza to find answers to common questions.

Global Regulation in Bacteria

Catabolite Repression

• The lactose operon is regulated by catabolite repression in addition to the lac repressor.
• Preferred Substrate: E. coli prefers glucose over other sugars.
• System Function:
  • If glucose is present, it represses lactose operon by removing a phosphate necessary for cyclic AMP (cAMP) production.
  • In the absence of glucose, phosphate accumulates, activating adenylate cyclase to convert ATP to cAMP.
  • cAMP binds to catabolite activator protein (CAP), promoting transcription of the lac operon.
• Key Concept: Even if lactose is available, the operon does not activate without cAMP and CAP.

Quorum Sensing

• Bacteria use quorum sensing to assess their population density and trigger specific gene expression.
• System Components: Two-component regulatory systems involving a sensor kinase and a response regulator.
  • Sensor Kinase: Detects environmental signals and phosphorylates itself.
  • Response Regulator: Activated by phosphorylation, can act as a repressor or activator.
• Example in Staphylococcus aureus:
  • AGR System: Used for quorum sensing in gram-positive bacteria.
  • AGRD: Synthesizes a pre-pro-peptide, processed by AGRB to produce an auto-inducing peptide (AIP).
  • AGRC-AGRA System: AGRC senses AIP concentration, phosphorylates AGRA, which activates quorum sensing genes.
  • RNA3 Regulation:
    • Acts as an antisense RNA to modify translation of various genes.
    • Activates translation by exposing Shindell-Garno sequences or inhibits by blocking them.

Regulation Influences

• Bacterial regulation has significant implications, e.g., in pathogens like enterohemorrhagic E. coli (EHEC).
• EHEC Regulation: Uses a two-component system responding to host signals (epinephrine/norepinephrine) to activate virulence genes.

Announcements

• Exam will be conducted in the usual classroom; review sessions scheduled for 2 PM on Saturday and Sunday.
• AGRB mutation discussions indicate that without proper peptide degradation, quorum sensing will not initiate.

These notes provide a structured summary of the lecture content focusing on regulatory mechanisms in bacteria and their implications. Review these topics to understand the complexities of bacterial gene regulation and its application in real-world contexts.