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Physiology Lect 9

Physiology Lect 9 Signal Transduction

1. Signal transduction is important for what processes? a. cell-cell communication b. a cell’s response to its environment c. intracellular homeostasis – internal communication
2. What are three types of targets within a cell and the response they elicit when signaled? a. metabolic enzyme – alters metabolism b. gene regulator – alters gene expression c. cytoskeletal protein – alters cell shape or motility
3. What sorts of molecules can function as ligands for signaling? Give an example of each? peptides/proteins - growth factors amino acid derivatives - epinephrine, histamine small biomolecules - ATP hormones - steroids, prostaglandins Gases - nitric oxide Photons - ray of sunlight Damaged DNA - Thing One Odorant - octyl acetate (orange s
4. Where are receptors for hydrophilic and hydrophobic signals found? hydrophilic are located on plasma membrane hydrophobic may be in cytosol or nucleus
5. What is the benefit of a hydrophilic signal vs. a hydrophobic signal? hydrophilic are faster
6. What are the possibilities for ligation? How do the multiple approach work? single ligand – single receptor dimerization – single ligand, 2 receptors trimerization – single ligand, 3 receptors the ligand usually brings the receptors closer together as they attempt to bind
7. How is information encoded? What does this encoding cause? structural changes can cause functional changes
8. What are the possible changes can a signal propagate? What regulates the signal pathway? amplification – one to many; signal spitting – bifurcation, trifurcation etc..;merging (integration) – the opposite of splitting; Feedback will regulate pathway
9. What are the general characteristics of plasma membrane receptors? proteins embedded in PM; one or more transmembrane anchors; single or polypeptide chains; ICF component alters cell activity; ECF portion contains binding site
10. When is the actual “transduction” of a signal? occurs when the ICF component responds to ligand bonding
11. When a ligand binds an ion channel-linked receptor what are the two possible responses? open or close
12. Ion channels receptors are critical to the function of what types of cells? neurons and muscles
13. What is the big example of an ion channel-linked receptor? what does it do? Where are they? AChR – acetylcholine receptor will open to allow sodium or calcium from the ECF to the ICF; located on motor endplates in ANS ganglia and CNS
14. The alpha protein of Gs binds to and activates what membrane enzyme? adenylyl cyclase
15. What does adenylyl cyclase do? How? removes two Phosphate groups from ATP and cyclizes it by creating bond between remaining; phosphate group and 3’ carbon of adenosine - cAMP
16. When a ligand binds to ECF receptor what change does this allow the trimeric G-protein to do? It binds the ICF portion of the receptor, then it exchanges a previously bound GDP for GTP, ditches it’s friends beta and gamma subunit, and halls ass to hook up with adenylate cyclase
17. When ditched by their friend alpha subunit, what do beta and gamma do? beta and gamma stick together cause they are BFF, remain in the membrane and may choose to stimulate ion channel-linked receptors
18. What makes shuts off alpha units selfish behavior toward beta and gamma reset to resting state? The intrinsic GTP-ase enzymatic activity of alpha subunit cleaves the terminal phosphate of GTP. When this is done it goes back to hang out with his friends beta and gamma
19. the alpha subunit of Gi does what to adenyl cyclase? inhibits the production of cAMP
20. What does the alpha subunit of Gq activate? a different membrane-bound enzyme, phospholipase C
22. The two major second messengers are?Who are the first messengers? cyclic AMP & ionic Calcium…the signaling molecules are sometimes called first messengers
23. Once created, cAMP frequently activates what enzyme? What does the enzyme do? protein Kinase A (PKA) – which phosphorylates either serine or threonine residues on proteins
24. How is PKA found the resting state within the cytosol? It exist as a dimer bound to a regulatory protein which keeps it inactive
25. Does cAMP actually bind to PKA to activate it? no, cAMP has an affinity for the regulatory/binding proteins. In the resting state, the intracellular concentration of cAMP is low and not pulled away from PKA. Once AC is stimulated to crank out cAMP intracellular concentration increases. The regulatory
26. In my awesome muscle cells how does epinephrine demonstrate this Gs cascade? a. Epi(NE)binds to the receptor (adrenergic) b. alpha Gs binds receptor, swaps GDP for GTP c. alpha activates AC, which makes cAMP d. cAMP allows PKA to break free from regulatory proteins and activate PKA e. PKA catalyzes the breakdown of glycogen to glu
27. Many genes have another DNA sequence that can be stimulated in the Gs pathway for transcription what is this? How does this pathway work? cAMP Response Element (CRE) upregulates transcription; a. PKA liberated from regulatory proteins moves to nucleus; b.PKA phosphorylates CREB b. CREB binds to CBP (CREB binding Protein); c. together CREB & CBP (now a heterodimer) bind to CRE to augment tra
28. Vibrio cholera produces a nasty little toxin that likes to bind where in the Gs pathway? Effect? a. It binds to takes ADP ribose from NAD; b. adds it to the alpha subunit of Gs.; c. This inhibits alpha subunits intrinsic GTP-ase activity.; d. AC remains active.; e. Overproduction of cAMP.; f. Massive Chlorine ion and water flow into GI diarrhea
29. What happens with Bordetella pertussis (Whooping Cough)? a. toxin ADP ribosylates alpha subunit of Gi; b. no inhibition of AC but for a different reason
30. Chronic Myelogenous Leukemia has a dysregulation that occurs how? a. fusion between long arms of chromosomes 9 & 22; b. creates new gene for unregulated tyrosine kinase called BCR-ABL; c. BCR-ABL instigates proliferation of cancerous white blood cells
31. What is the G-protein that uses calcium ions as second messengers? What enzyme does it use? Gq works through enzyme phospholipase C-beta (PLD-Beta)
32. What is the signal cascade for Gq? alpha subunit activates PLC; cleaves into DAG and IP3; DAG stays in the membrane and docks with PKC; IP3 diffuses into cytosol, opens Ca channel on ER; Ca ions bind to DAG-PKC complex, activates it; Activated PKC phosphorylates cell targets such as:MAPK
33. What happens in another pathway if four calcium ions bind their beatch calmodulin? calcium-calmodulin complex activates Ca-calmodulin-dependent protein kinases (CaM-kinases) These are active in smooth muscle contraction;
34. Cancer cells often lose their ability to adhere because of failure in what type of receptor? enzyme-linked receptors
35. What are the two types of enzyme-linked receptors? kinases & phosphatases
36. How does an enzyme linked tyrosine receptor operate? what is different from the G-protein receptor? a. the G-protein may be activated by a single ligand; b. tyrosine kinases prefer dimer, trimer, oligomer/polymer ligands; c. cross links are formed between several receptors – di/tri/oligomerization; d. This created aggregates that will autophosphylate
37. When the autophosphylation occurs on receptor tails on the ICF side what happens? Outside? if on ICF usually increases the kinase activity; if on ECF usually creates a docking site for other proteins
38. What is a motif? a specific amino acid sequence to which protein domain binds
39. What is one of the most important domains? Why? How? SH2 allow RAS to be activated; A protein such as GRB-2 has an SH2 and SH3 domain at each end.; b. the SH2 end docks with phosphorylated Tyrosine kinase; c. This encourages binding to the SH3 domain by GEF; d. GEF (now on SH3) helps RAS swap GDP for GTP;
40. How did we used to view cell activity responsible for cancer? a cell was at rest until activated, then deactivated by removal of ligand, drifting away of ligand, metabolizing of ligand, sequestering of ligand etc..; Cells that did not deactivate were trouble…ie cancer chronic activation
41. What do we now know about cancer cells and signaling? there are activating and inhibiting signals cells with faulty inhibitory mechanisms are phosphatase linked
42. What is an key family of inhibitory receptors? How do they work? NK cells destroy invaders or damages body cells; NK’s display KIR on their surface; KIR bind MHC I proteins on normal cells. this deactivates the NK by signaling for a phosphatase to inhibit the activation signal; bacterial and mutated/damaged cells do no
Created by: MichaelR



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