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Lecture 13

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BIOL 2021
Patricia Lakin- Thomas

February 28, 2013 Lecture 13: Cell Communication Calcium  Calmodulin (Fig 15.43) o 4 binding sites for Ca2+ o Changes conformation with Ca2+, binds to other proteins o Targets: Enzymes, membrane transport proteins, protein kinases o CAM Kinases  Ca2+/Calmodulin dependant kinases  Phosphorylate other proteins  Gene regulatory proteins  Seriene/Threonine Kinases G Protein Regulated Ion Channels  G Proteins regulate by: Direct binding, or indirectly through cyclic nucleotides  Cyclic Nucleotide gated-ion channels (smell and vision)  Rod Photoreceptor cells (Fig. 15.48) o Rods – vision in dim lighting o Photoreceptor is rhodopsin (G-protein coupled receptor) (GPCR – Fig 15.16B) o Ligand is light o Retinal isomerisation – Fig 3-53A AND pretty picture on Wikipedia o Light + 11-cis  tutto-trans retinal  Conformational change in rhodopsin o Causes a change in G protein t G – transducin o Activates enzyme cyclic GMP phosphodiesterase  Destroys cGMP (Fig 15-47)  cGMP made by guanylylcyclase  Plasma membrane around discs has cGMP gated ion channels o Figure 15.49 o Dark – High cGMP, channels open, cells depolarized, high rate of transmitter release o Light – Destruction of cGMP, channels close, hyperpolariszes, transmitter release decreases  Signal  brain  light  Signalling Cascade o Amplification – Fig 15.50  Adaptation o Receptor desensitization – Fig 15.51 (1) Activated receptor phosphorylated (Kinase is GPCR Kinase) (2) Arrestin Protein binds, prevents binding to G-proteins Enzyme Coupled Surface Cell Receptors  Similar to GPCRs o Transmembrane proteins bind to ligand on outer PM  Differences: o Cytosolic domain has enzyme activity or associates with an enzyme o Only ONE transmembrane domain  Receptor Tyrosine Kinases o Tyrosines (not Ser/Thr) – examples on Fig 15.52 and Panel 3.1 o Cell survival, growth, division, Epidermal growth factor, insulin, nerve growth factor, etc o Ligands – extracellular signal proteins or memb bound ligand on another o Ephrin = contact – dependant signal o Activation of RTKs by dimerization (Fig 15.53A)  Ligands – symmetric dimers, 2 binding sites  2 receptors dimerize  Phosphorylate each other - trans auto phosphorylation  Effects :  Increase kinase ac
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