Signal Transduction Pathways

Introduction

• Presenter: Mr. Andersen
• Video Number: 38
• Topic: Signal Transduction Pathways
• Importance: Critical for cellular actions but sometimes misunderstood.
• Analogy: Comparing to Jimi Hendrix's guitar playing
  • Guitar strings vibrate and are transduced into electrical signals via pickups.
  • Signals amplified via amplifier.
  • In cells, chemical messages are transduced into cellular actions and can be amplified.

Basics of Signal Transduction Pathways

• Message: Comes in the form of a chemical message.
• Transduction: Conversion of an external signal into actions within the cell.
• Amplification: Signal can be amplified for larger cellular response.
• Phosphorylation Cascade: Key mechanism involving the transfer of phosphate groups.
  • Protein Kinase: Enzymes critical in phosphorylation cascades.
• Modification: Sometimes direct alteration of a protein.

Example Pathway: Epinephrine in Liver Cells

• Message: Epinephrine
  • Origin: Adrenal gland
  • Target: Liver cells to release glucose from glycogen.
• Step-by-Step Process:
  1. Epinephrine docks with a G-protein receptor on the cell membrane.
  2. Conformational Change: Shape of the receptor changes.
  3. Alpha Subunit: Released from the G-protein and binds to adenylyl cyclase, activating it.
  4. Adenylyl Cyclase: Converts ATP to cyclic AMP (cAMP).
  5. cAMP: Secondary messenger, diffuses within the cell.
  6. Protein Kinase Activation:
     • cAMP binds to regulatory subunits, releasing catalytic subunits.
     • Catalytic subunits become phosphorylated (activated).
  7. Phosphorylation: Catalytic subunits phosphorylate and activate other enzymes, such as phosphorylase.
  8. Result: Release of glucose from glycogen.
• Deactivation: Pathway shuts down when the ligand (epinephrine) is no longer present.

Detailed Review

• Epinephrine: Ligand, cannot enter the cell, attaches to receptor.
• G-protein: Embedded in cell membrane, has alpha subunit that initiates signal cascade.
• Adenylyl Cyclase: Enzyme activated by alpha subunit, converts ATP to cAMP.
• cAMP: Activates protein kinase by binding to regulatory subunits, releasing catalytic subunits.
• Amplification: Multiple cAMP molecules can activate many protein kinases, amplifying the signal.
• Phosphorylation: Catalytic subunits phosphorylate enzymes, enabling cellular responses such as glycogen breakdown.

Summary

• Signal Transduction Pathway: Converts an external signal into a cellular response.
• Analogy Recap: Like playing the electric guitar, where the signal is amplified to produce a significant output.