L9 - There are three classes of cell surface signaling...

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There are three classes of cell surface signaling receptors Enzyme-linked receptors
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PLC β results in the release of calcium: a ubiquitous intracellular messenger In order for calcium to function as a messenger, intracellular levels of calcium have to remain low. Multiple way to remove calcium from the cell.
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Example of calcium signaling: binds and activates calmodulin -very abundant -4 high affinity Ca+ + binding sites--2 or more must bind (basic principles- coop binding of messengers for activation) switch- like activation -calmodulin itself has NO activity--it us used to activate other enzymes
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Activated calmodulin binds and activates calmodulin-dependent protein kinase -large complex of 12 subunits--only 1 shown Without calmodulin-- inhibitory conformation Binding of Ca++/calmodulin allows catalytic domain of the protein to phosphorylate the inhibitory domains of neighboring subunits Then it also phosphorylates other proteins in the cell
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Calcium/calmodulin-dependent protein kinase plays an important role in memory formation
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G protein coupled signaling by endo cannabinoids and exocannabinoids (pot) Post-synaptic depolarization open V-G Ca++ channels. Ca++ activates enzymes that synthesizes endocannabinoids from lipids --likely through DAG and the arachidonic acid pathway Endocannabinoids leave the cells and activate PRE-synaptic CB1 receptors Activated G-protein releases α and β , γ subunits. β , γ subunits blocks Ca++ channels This, in turn, decreases the probability of transmitter fusion and release
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G protein coupled signaling by endo - cannabinoids and exocannabinoids ( pot ) These CB1 synapses are often GABAergic or INHIBITORY so this phenomenon is called “depolarization induced suppression of inhibition” These GABAergic interneurons control plasticity at excitatory synapses--that is to say in principle endocannabinoids can increase LTP or excitatory transmissions by inhibiting the inhibitor. Question: does it promote learning and memory? Complex Answer. In both mice and humans, endocannabinoid both enhance and impair memory depending on the test used.
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There are 6 kinds of enzyme-linked receptors: 1) Receptor tyrosine kinases 2)Tyrosine kinase associated receptors 3)Receptor guanalyl cyclases 4)Receptor tyrosine phosphatases 5)Receptor serine/threonine kinases 6) Histodine kinase associated receptors
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Examples of receptor tyrosine kinases
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Receptor tyrosine kinases are activated by binding of ligand, which induces dimerization. 3 ways cross-linking achieved A) Ligands like PDGF is a covalently linked dimer with 2 receptor binding sites. B) Ligands like FGF bind in clusters to proteoglycans which allow receptors to cross-link.
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Receptor tyrosine kinases are activated by binding of ligand, which induces dimerization and autophosphorylation.
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