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Cell Communication

Cell Communication. Chapter 11 - Abridged. Cell-to-Cell Communication. Critical for multicellular organisms Trillions of cells must communicate in order to coordinate their activities Recent research indicates: cancer results from corrupted communication Unimportant for the AP Exam

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Cell Communication

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  1. Cell Communication Chapter 11 - Abridged

  2. Cell-to-Cell Communication • Critical for multicellular organisms • Trillions of cells must communicate in order to coordinate their activities • Recent research indicates: cancer results from corrupted communication • Unimportant for the AP Exam • Crucial for understanding the breakthroughs in cancer and genetics that are occurring almost monthly now

  3. Recent Nobel Prizes in Medicine • 2001 – Hartwell, Hunt, & Nurse – cyclin pathways and cell cycle regulation (yeast) • 2002 – Brenner, Sulston, Horvitz – used C. elegans to elucidate the mechanism of apoptosis • 2006 – Fire & Mello - used C.elegans to discover the pathway of RNA interference

  4. Simon Sez… • Signaling is a lot like the game “Simon Says…” • The signal is received: the game players hear: “Simon says take a step forward” • The signal is transduced: players must decide whether to step forward or not • The signal elicits a response: players step forward if the command was preceded by “Simon says”

  5. 3 Stages of Signaling • Thesis: external signals are received & converted to responses within the cell 1. Reception • Signaling molecule binds to receptor protein = Shape Change 2. Transduction • Cascades of molecular interactions relay signals from receptor proteins to target molecules in the cell 3. Response • Regulation of transcription or cytoplasmic activities

  6. 1st form of signaling •  Yeast (fungi) mating • Process: • Release mating factor • Receive complementary factor • ???? • Response: grow toward opp. Type • Nuclei fuse = genetic recombination

  7. Overview of Cell Signaling

  8. View Animation • 11_06 SignalingOverview_A.swf

  9. Reception • Reception involves getting the signal to the correct receiver • Only certain cells have the correct receptor = only certain cells can receive the signal • Signaling molecule usually called ligand • receptor-ligand binding causes a conformational change in the receptor molecule (remember induced fit?) • Conformational change = Activation of the receptor molecule

  10. 2 Types of Signal Receptors 1. Plasma Membrane Receptors • Hydrophilic or water-soluble ligands or signal molecules • G Protein-Coupled Receptors (GPCR) • Receptor Tyrosine Kinase (RTK) • Ion Channel Receptors 2. Intracellular Receptors  Hydrophobic or Nonpolar ligands  Carry out transduction by themselves

  11. View Animation • 11_13SignalTransduction_A.swf

  12. G Protein-Coupled Receptor

  13. Receptor Tyrosine Kinase (RTK) • Amplification • Kinase = enzyme for transfer of phosphate group

  14. Ligand-Gated Ion Channel • Membrane receptor with a region that acts as a “gate” when the receptor changes shape. •  When the signal molecule binds, gate opens or closes •  Important in the nervous system

  15. IntracellularReceptor  Hydrophobic signal molecules  Testosterone  Most intracellular receptor signals do the entire transduction on their own  Testosterone behaving as a transcription factor -- controls which genes (DNA) are transcribed into mRNA

  16. Transduction • Multistep Pathway • Transduction = shape change • Signal amplification • Signal Transduction Pathways often involve a phosphorylation cascade • Molecule is phosphorylated = activated • Phosphate removed = deactivation

  17. Protein Kinases (PK) -- enzymes that transfer phosphate groups Protein Phosphatases (PP) -- enzymes that remove phosphate groups

  18. Second Messengers • 1st messenger = receptor • Only GPCR & RTK have 2nd messengers • Other important component of transduction pathways • Most components are enzymes or proteins • Small & polar • Calcium Ions & Cyclic AMP • Initiate a phosphorylation cascade

  19. Response • Response may occur in the cytoplasm or nucleus • 2 Types of typical response: 1. Enzyme activity is regulated (turned on or off) 2. Synthesis of enzymes is regulated (promoted or inhibited)  Transcription Factors – control which genes are transcribed (DNA  RNA)

  20. Transcription Factors

  21. GF = Growth factor RTK = Receptor Tyrosine Kinase Ras = G Protein Associated with tumor growth Rho = G protein

  22. RTK = Receptor Tyrosine Kinase GPCR – G-protein coupled receptor PDK1 = Protein dehydrogenase kinase Akt = Protein kinase -- Involved in apoptosis Apoptosis = Programmed cell death

  23. Day 1 Complete

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