Cell Communication

1. Cell Communication The language of chemistry

2. What do cells talk about? • Sex • Danger • Action • Recovery

3. Evolution of cell signaling • Yeast and mammals signaling mechanisms are very similar • Why? • Pathway evolved in common ancestor

4. local calls • Cell junctions connect adjoining cells • Chemical signals dissolve into cytosol • Membrane bound surface proteins • Coordinates actions of multiple cells • Ex. Embryonic development

5. In state calls • Signaling cell releases molecular messages • Bind to receptors on receiving cell • Growth factors • Synaptic signaling

6. Long distance calls • Glands release hormones into the bloodstream • Insulin, epinephrine (adrenaline), testosterone, etc • Plant hormones diffuse through cells or through the air • Ethylene, growth factors

7. The gist of it: • Reception • Transduction • Response

8. An example • Fight or flight response • Reception-E. binds to receptors on the surface of liver cells • Transduction-glycogen phosphoylase is activated • Response-enzyme breaks glycogen into glucose, glucose is released into the bloodstream

9. Reception • Only cells with the correct receptor protein will be able to “hear” the message • Signaling molecule binds to receptor, changes its shape

10. Intracellular receptors • Small, hydrophobic molecules pass through cell membrane • Bind to receptor inside of cell • Turn on specific genes • Nitrous oxide • Steroid hormones

11. Extracellular receptors • Water soluble signaling molecules bind to membrane bound receptors • Ion channel receptors in nerve cells

12. Transduction • Protein interactions pass message from receptor to response • Multiple steps allow signal to amplified

13. Protein phosphorylation • Kinases transfer phosphates from ATP to proteins • Phosphorylation changes shape of protein • Consumes ATP, uses energy • Protein phosphatases remove phosphates, turn off signal

15. cAPM • Cyclic Adenosine Monophosphate • Binding of signal molecule activates enzyme that turns ATP Into cAMP(20fold increase/seconds) • Ex. Epinepherine stimulates cAMP production, cAMP stimulates proteins associated with fight or flight response • Once signal has passed cAMP is degraded to AMP Cholera- toxin stimulates cAMP production. Overstimulates transport proteins in intestine

16. Response • Final action • Opening/closing of ion channel • Activation of enzyme • RNA synthesis/ protein production • Signal can be amplified at each step of pathway • Activates multiple molecules before breaking down

18. Differential responses • Different cells make different proteins • Receptors, transducers, response proteins • Ex. Heart vs. liver response to epinephrine • Heart= contraction • liver= glycogen metabolism

19. But it isn’t that simple… • Proteins participate in more than one pathway • Scaffolding proteins hold multiple kinases • Pathways branch, one signal causes multiple responses • Pathways interact, two signals cause the same response

20. Termination • All changes are reversible • As concentration of signaling molecules decreases response needs to decrease • Enzymes convert relay proteins back to inactive form • Ex. Cholera results when signaling pathway remains on indefinitely