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Ch. 15 - Cell Communication - Part 3 A summary of the chapter and lecture notes on cell communication, part 3. Includes illustrations and graphics from the textbook.

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BIOL 2021
Julie Clark

st BIOL 2021- April 21 2009 CHAPTER 15: CELL COMMUNICATION III G PROTEIN REGULATED ION CHANNELS - Binding directly or indirectly through a cyclic nucleotide VISUAL CASCADE - Rod photoreceptors - vertebrates - Fastest known G protein response DIM LIGHT VISION - Photo receptor= rhodopsin= GPCR - Ligand = light – delta in conformation - Retinal absorbs light - II cis retinal – (light isomerisation)-> all trans retinal - ∆ in Gt= transduction - Activates cyclic GMP phosphodiesterase - cGMP: made by guanylyl cyclase  destroyed by cGMP posphodiesterase Figure: cGMP - Dark: high cGMP, ion channels OPEN, depolarized cell, high rate of transmitter - cGMP gated ion channels - Light: cGMP decreases, ion channels CLOSE, hyperpolarizes, transmitters decrease, signal to brain -> light Figure: phototransduction SIGNALLING CASCADE - Amplification - One photon of light Figure 15-50: amplification in light transduction ADAPTATION - Turn signal down - Receptor desensitization - Signal is still present - GPCR kinase phosphorylates activated receptor -. Arrestin binds to block G protein ENZYME COUPLED CELL SURFACE RECEPTORS - Similar to GPCR:  Trans membrane protein- bind ligand on outside  Differences: cytosolic domain has enzyme activity OR directly binds on enzyme. One transmembrane domain. Receptor tyrosine kinase (RTK) - Phosphorylates on tyrosine on substrates themselves= autophosphorylation  Ligands are extracellular proteins - Cell survival, growth division OR protein on another cell - Ephrins  Contact-dependant signalling Table 15-4: some proteins that act through RTK ACTIVATION BY DIMERIZATION - Ligand binding two receptors dimerize - Transautophosphorylation  2 results: 1) increase kinases activity 2) creates docking sites for other proteins - From signalling complex  Activated docked protein by phosphorylation or by docking  Domain= SH2 domain  Src homology  Phosphotyrosine binding - Docked protein?  Enzymes or adaptor proteins  Couple RTKs to other proteins Ras Protein - Large family activated by RTKs using adaptors - Monomerize GTPase: active= GTP bound  Inactive
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