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Chemical Signaling Between Cells. 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)
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Chemical Signaling Between Cells • 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
Note how specificity is determined by receptor protein Note dependence on Systemic Circulation (blood/lymph) Long-Distance Diffusion
Local Diffusion e.g., Histamine released from damaged cells in inflammation e.g., Interferon release by viral-infected cells
Note both absence of and lack-of-dependence on Systemic Circulation Local Diffusion
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 chemical signals We will not dwell on the purpose of the signal We also will not dwell on why and how a given cell released a given signal
Three Stages of Signal Transduction • Reception of extracellular signal by cell • Transduction of signal from outside of cell to inside of cell—often multi-stepped • Note not necessarily transduction of ligand • Cellular Response • Response is inititiated and/or occurs entirely within receiving cell
1. Reception 3. Response Three Stages 2a. Transduction 2b. Transduction 2c. Transduction 2d. Transduction Responses usually involve increasing or decreasing some Protein’s Function
Three Stages 1. Reception 2a. Transduction 2b. Transduction 3. Response
Various Responses Note that more than one response can result from the reception of a single ligand
Ligands e.g., nitric oxide e.g., steroid hormones
Extracellular Reception e.g., insulin e.g., epinephrine
G Protein-Linked Receptors the more ligand binding, the greater the cellular response note how activation is reversible
G Protein-Linked Receptors note how activation is reversible
the more ligand binding, the more K+ in cytoplasm G Protein-Linked Receptors
Tyrosine Kinase Receptors • Note steps involved: • Ligand Reception • Receptor Dimerization • Catalysis (Phosphorylization) • Subsequent Protein Activation • Further Transduction • Response
Note how, via catalysis, one ligand molecule binding gives rise to many new intracellullar molecules Signal Amplification (Cascade)
Phosphorylation Cascade • This reversibility contributes to the dynamic nature of cells: • A protein that is activated by a Protein Kinase in turn is inactivated by a Protein Phosphatase • This means that the effect of signals can’t last forever • For the cellular response to continue, more signal must be received
100 molecules 102 molecules 104 molecules 104 molecules 105 molecules 106 molecules Epinephrine Glycogen Breakdown 108 mol Glu-1-Phosphate
Specificity of Cell Signaling • Note how same ligand gives rise to different responses • Cells differ in terms of their proteins • Different proteins respond differently to the same environental signals • (note, though, same receptors, different relay) • Different cells behave differently because some, but not all proteins can differ between cell types
Acknowledgements biology.ucf.edu/courses/bsc2010/08-2010C-02.PPT www.aw.com/bc/ppt/marieb_ap/chap03c.ppt http://zeus.uwindsor.ca/courses/biology/zielinski/204/comm1.ppt http://vaccine.chonbuk.ac.kr/images/cell/Chapter%2015%20Cell.ppt http://faculty.uca.edu/~jmurray/BIOL1440/lec/lec15.ppt \http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/7-signal.ppt http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/9-glycogen.ppt http://homepage.smc.edu/chen_thomas/Bio21/Chpt%2011%20Cell%20Comm.ppt
the more ligand binding, the more K+ in cytoplasm G Protein-Linked Receptors