Introduction

• Discussion regarding the exam and review session format.
  • Potential for doing one lecture over Zoom.
  • The possibility of uniform grading based on same exam questions.
• Key question addressed: Describe membrane structure.

Exam Format and Expectations

• Questions may be asked on pathways studied in class.
• Expectation to describe scenarios of receptor activation leading to gene expression changes.
• Examination structure allows for written descriptions or diagrams.
  • Starting point: ligand binding to a receptor.
  • Endpoint: activation of a transcription factor.
• Emphasis on understanding pathways without needing to memorize specific details.

Technical Details of Pathways

• Overview of the day's lecture focusing on GPCRs (G Protein-Coupled Receptors) and various intracellular pathways.
• GPCRs and their importance in physiological processes, illustrated through examples.

GPCR Pathways

Smell Pathway

• Example of GPCR involvement in olfaction:

  • Odorant molecules bind GPCRs in the nose.
  • GPCR activation leads to G-protein alpha subunit activation.
  • Activated alpha subunit stimulates adenylyl cyclase, converting ATP to cyclic AMP (cAMP).

• Dual action of calcium and sodium channels:

  • Induces action potential signaling to the brain.
  • Activates Protein Kinase A (PKA).

• Role of PKA in transcriptional activation:

  • PKA influences the transcription of specific genes in response to odors.
  • Physiological responses to smells involving gene expression changes.

Dopamine Signaling via GPCR

• Another GPCR pathway’s influence on dopamine signaling:
  • Signaling molecule binds GPCR, activating G-protein.
  • G-protein activates adenylyl cyclase, leading to cAMP generation.
  • cAMP activates PKA, which then activates CREB (a transcription factor).
  • CREB engages with DNA to initiate transcription influenced by dopamine signaling.

Phospholipase C Activation via GPCR

• General pathway cycle from GPCR to phospholipase C:

  • Receptor binding activates G-protein, leading to phospholipase C activation.
  • Phospholipase C cleaves PIP2 into IP3 and DAG.
  • IP3 promotes calcium release from the endoplasmic reticulum (ER).
  • DAG, in concert with calcium, activates Protein Kinase C (PKC).
    • PKC plays a role in various signaling pathways and muscle contractions.

• Summary of GPCR pathways activation context:

  • GPCR may activate either adenyl cyclase or phospholipase C, depending on cellular conditions.

Receptor Tyrosine Kinase (RTK) Mechanisms

Epidermal Growth Factor Receptor (EGFR)

• EGFR as a well-studied member of RTKs regulating skin growth.

• Mechanism of EGFR activation:

  • EGF binding induces dimerization of RTK.
  • Dimerized RTK autophosphorylates tyrosines.

• Subsequent binding of proteins to RTK:

  • GRB2 (an adaptor protein) binds RTK through its SH2 domain.
  • The SH3 domain engages SOS, which is a GEF (Guanine nucleotide Exchange Factor).

• Activation of the RAS pathway:

  • SOS activates RAS by exchanging GDP for GTP.
  • Active RAS binds to RAF, another kinase.
  • RAF phosphorylates MEK, which in turn phosphorylates MAP kinase.

• Detailed signaling cascade:

  • MAP kinase pathways lead to transcription activation in response to various signals.
  • RTK signaling pathways are vital since they are implicated in cancer-related processes.

Summary of Concepts and Preparation for Exam

• Understanding expected pathways to explain membrane receptor activation and gene expression changes.

  • Flexibility in answers is permitted, as long as scientific rationale is sound.

• Knowledge required for exam preparation:

  • Different types of G proteins (trimeric vs. monomeric).
  • Mechanisms of active transport vs. diffusion vs. facilitated diffusion.
  • Differentiation between various junctions (gap junctions, anchoring junctions, tight junctions).
  • Recognition that many tested topics stem from previous lectures.

Conclusion

• Reminder of the necessity to grasp fundamental mechanisms involving membrane receptors and intracellular signaling pathways as well as their relevance in biology and associated disorders such as cancer.
• Mention of a paper due for review, maintaining focus on integrating lectures with study materials for comprehensive understanding.