Chapter 11: Cell Communication

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Chapter 11: Cell Communication

  1. 1. Chapter 11:Cell Communication
  2. 2. Signal-Transduction Emphasis  This chapter’s emphasis is on signals that are released from one cell and allowed to freely diffuse to a second (or more) recipient cell(s)  These communications are deliberately initiated, received, and interpreted in order to increase the physiological coordination of the cells in multicellular organisms  We will consider in particular those events that follow the reception of a chemical signal  We will not dwell on the purpose of the signal  We also will not dwell on why and how a given cell releases a given signal
  3. 3. Signaling with Direct Contact
  4. 4. Local Signaling w/o Direct Contact e.g., interferon release by viral-infected cells
  5. 5. Long-Distance Signaling
  6. 6. Long-Distance Diffusion Note how specificity is determined by presence/absence of receptor protein
  7. 7. Signalling, Free-Living Cells
  8. 8. Cell-Cell Chemical Signaling  Three general categories of chemical signaling: • Cytoplasmic connections between cells • Cell-to-cell contact-mediated signaling • Free diffusion between cells •Distant cells (hormones) •Adjacent cells (within interstitial space)  All of latter involves the physical movement of ligands • That is, ligand reception by a protein • Note that reception means molecule-to- molecule contact
  9. 9. e.g., nitric oxide e.g., steroid hormonesLigands e.g., insulin Nothing to e.g., epinephrine memorize on this page
  10. 10. Signal Transduction Often turning on or off enzyme activity In this case the receptor proteinLigand is a membrane protein
  11. 11. Three Stages 1. Reception 2a. Transduction 2b. Transduction 2c. Transduction 2d. Transduction 3. ResponseResponses usually involve increasing or decreasing some protein’s function
  12. 12. Three Stages 1. Reception 2a. Transduction 2b. Transduction 3. Response
  13. 13. Intracellular Receptor
  14. 14. Rapidity of Response Slower response if requiring protein synthesis
  15. 15. G-Protein-Linked Receptor bind GTP G proteins
  16. 16. G-Protein-Linked ReceptorThe more ligand binding, the greater the cellular response Note lability of all signals
  17. 17. Protein Kinase & Phosphatase Protein Kinase O Protein OH + ATP Protein O P O + ADP O Pi H2O Protein Phosphatase Therefore, res Like signal This ponses tend to lability, reversib reversibility continue (or ility of contributes expand) only phosphorylatio to the so long as n makes dynamic signaling signaling nature of continues reversible cells
  18. 18. Tyrosine Kinase Receptor
  19. 19. Receptor Tyrosine KinaseNote steps involved:1. Ligand Reception2. Receptor Dimerization3. Catalysis (Phosphorylization)4. Subsequent Protein Activation5. Further Transduction6. Response
  20. 20. Ion-Channel Receptor Reversibility is assured by pumping ions back out again (using separate protein)
  21. 21. Phosphorylation Cascade
  22. 22. Cyclic AMP (cAMP) Note reversibility “Second”Messenger Second messengers are not proteins
  23. 23. 2nd Messenger, S.T.P.
  24. 24. Ca2+-mediated Signal Amp. Releasing Ca2+ is a means of greatly amplifying signal
  25. 25. Signal Amplification (Cascade)
  26. 26. Signal Amplification (Cascade) Note how, via catalysis, one ligand molecule binding gives rise to many new intracellullar molecules
  27. 27. Signal Amplification (Cascade)
  28. 28. Signal-Transduction Cascade Seek to understand the concept, rather than memorize the specific protein
  29. 29. Nuclear Response
  30. 30. Various Responses Note that more than one response can result from the reception of a single ligand
  31. 31.  Same ligand gives rise toVarious Responses different responses  (here same receptor, different relay)  Cells differ in terms of their proteins  Different proteins respond differently to the same environmental signals
  32. 32. The End

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