Chapter 11: Cell Communication

1. Chapter 11:Cell Communication

2. Important Point: If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!

3. 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 Signal-Transduction Emphasis

4. Signaling with Direct Contact

5. Local Signaling w/o Direct Contact e.g., interferon release by viral-infected cells

6. Long-Distance Signaling

7. Note how specificity is determined by presence/absence of receptor protein Long-Distance Diffusion

8. Signalling, Free-Living Cells

9. 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 Cell-Cell Chemical Signaling

10. Ligands e.g., nitric oxide e.g., steroid hormones Nothing to memorize on this page e.g., insulin e.g., epinephrine

11. Signal Transduction Often turning on or off enzyme activity In this case the receptor protein is a membrane protein Ligand

12. 1. Reception 3. Response Three Stages 2a. Transduction 2b. Transduction 2c. Transduction 2d. Transduction Responses usually involve increasing or decreasing some protein’s function

13. Three Stages 1. Reception 2a. Transduction 2b. Transduction 3. Response

14. Intracellular Receptor

15. Slower response if requiring protein synthesis Rapidity of Response

16. G-Protein-Linked Receptor G proteins bind GTP

17. G-Protein-Linked Receptor The more ligand binding, the greater the cellular response Note lability of all signals

18. Protein Kinase & Phosphatase Therefore, responses tend to continue (or expand) only so long as signaling continues This reversibility contributes to the dynamic nature of cells Like signal lability, reversibility of phosphorylation makes signaling reversible

19. Tyrosine Kinase Receptor

20. Receptor Tyrosine Kinase • Note steps involved: • Ligand Reception • Receptor Dimerization • Catalysis (Phosphorylization) • Subsequent Protein Activation • Further Transduction • Response

21. Ion-Channel Receptor Reversibility is assured by pumping ions back out again (using separate protein)

22. Phosphorylation Cascade

23. Note reversibility Cyclic AMP (cAMP) “Second” Messenger Second messengers are not proteins

24. 2nd Messenger, S.T.P.

25. Ca2+-mediated Signal Amp. Releasing Ca2+ is a means of greatly amplifying signal

26. Signal Amplification (Cascade)

27. Note how, via catalysis, one ligand molecule binding gives rise to many new intracellullar molecules Signal Amplification (Cascade)

28. Signal Amplification (Cascade)

29. Signal-Transduction Cascade Seek to understand the concept, rather than memorize the specific protein

30. Nuclear Response

31. Various Responses Note that more than one response can result from the reception of a single ligand

32. Same ligand gives rise to different responses • (here same receptor, different relay) • Cells differ in terms of their proteins • Different proteins respond differently to the same environmental signals Various Responses

33. The End