Chapter 16 Cell Communication Focus will be on mechanisms and pathways of ‘Signal Transduction’

1. Chapter 16 Cell Communication Focus will be on mechanisms and pathways of ‘Signal Transduction’ -- How cells communicate an external signal across the cell membrane You will not be responsible for: Details of Nitric oxide (NO) action Down-stream signaling events i.e., topics on pp 558-567 -- we will cover these selectively Questions in this chapter you should be able to answer: Chapter 16:1 - 10 11all but e, 12,13,16,17,18, 19, 20, 22, 24, 25 Cell Communication

2. How do cells communicate with each other? Signaling mechanisms Signaling responses Cell Communication

3. EGF What types of molecules carry signals to cells? 1) Gases (really small) NO, H2S, CO 2) ‘Smallish’ organic molecules steroids neurotransmitters [drugs/poisons (nicotine, phytohormones, etc)] 3) Peptide hormones (much bigger) Cell Communication

4. Where are the receptors? Intracellular receptors vs Cell-surface receptors Cell Communication

5. How do cell surface receptors function? Signal transduction Pathways Signaling proteins Secondary Signals -- cAMP, Ca++, DAG, IP3 FSH & receptor Cell Communication

6. Signaling pathways can interact Multiple signaling pathways can be activated simultaneously Signal integration Cell Communication

7. What are the three types of cell surface receptors? = Ligand-gated channel Cell Communication

8. How are G-proteins activated? • “7-pass” receptors • -- Hundreds of different types • -- triggering enumerable different • cytoplasmic processes • Examples • Glucagon – activates glucose release by liver • Lutenizing Hormone (LH) – triggers progesterone • release from ovary • Adrenalin (epinephrine) – increases heart rate • Allergen – mast cell degranulation G-protein-linked receptors Cell Communication

9. How do activated G-proteins trigger release of ‘secondary messenger’ molecules? -- open channels -- activate enzymes Secondary messengers include: cAMP, Ca++, DAG, IP3 Some toxins interfere with G-proteins Cholera toxin Inhibits GTPase activity of α-subunit -- causes Na+ efflux into intestine -- water flow into intestine Pertussis toxin Prevents GDP/GTP exchange -- GTP locked in off state -- mucous secretion into lungs cAMP signaling Cell Communication

10. Acetylcholine acts at a G-protein-linked receptor on heart muscle to make the heart beat more slowly by the effect of the G protein on a K+ channel, as shown in this Figure. Which one or more of the following would enhance this effect of acetylcholine? Explain. (a) A high concentration of a non-hydrolyzable analog of GTP. (b) Mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine. (c) Mutations in the G protein α-subunit that speed-up the hydrolysis of GTP. (d) Mutations in the K+ Channel that make the βγ-subunit bind tighter Cell Communication

11. Retina contains G-protein coupled light receptors Rod cells Activation ↓ Na+ flow Na channel gated by cGMP Rhodopsin Transducin (G-protein) -- activates cGTP phosphodiesterase ΔMembrane potential Question 16-8 P 556 Cell Communication

12. How do enzyme-linked receptors function? Receptor Tyrosine Kinases (RTK) Dimerization Autophosphorylation Activated signaling proteins Cell Communication

13. RTK Signaling often occurs through Ras A “monomeric” GTP-binding protein Mutated ras can be an ‘oncogene’ Some activate STATs -- act as gene regulators -- fast response Notch – even faster Cell Communication

14. How are complex signally pathways ‘dissected’? Genetically engineer cells to contain… -- Knockout mutations -- Constitutive expression mutations How do these 5 experiment establish signaling sequence of RAS, X and Y? Cell Communication

15. When activated by the signal, the platelet-derived growth factor (PDGF) receptor phosphorylates itself on multiple tyrosines (as indicated below by the circled Ps; the numbers next to these Ps indicate the amino acid number of the tyrosine). These phosphorylated tyrosines serve as docking sites for proteins (A, B, C, and D) that interact with the activated PDGF-receptor. Binding of PDGF activates the PDGF-receptor leading to an increase in DNA synthesis. To determine whether protein A, B, C, and/or D are responsible for activation of DNA synthesis, you construct mutant versions of the PDGF-receptor that retain one or more tyrosine phosphorylation sites. In the cells, the various versions of the PDGF-receptor become phosphorylated on whichever tyrosines remain. You measure the level of DNA synthesis in cells that express the various mutant receptors and obtain the data shown below. • From these data, which, if any, of these proteins A, B, C, and D are involved in the stimulation of DNA synthesis by PDGF? Why? • Which, if any, of these proteins inhibit DNA synthesis? Why? • Which, if any, of these proteins appear to play no detectable role in DNA synthesis? Why? • What is the effect of the binding of A on the effect of B? Cell Communication