Lecture 5 Synaptic Transmission

G protein systems relatively small just a receptor

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G-Protein Systems ((relatively small. Just a receptor not a lot of biological functions in itself,but link to biochemical pathways.) o G-protein-coupled receptor 1 polypeptide/ 1 subunit 7 membrane spans binds to G protein binds NT 2 functions – has to interact with NT and G protein o G-Protein (much more complex) 3 polypeptides/subunits (can have functionally distinct effects on other parts of the cell) binds to G-protein-coupled receptor binds guanosine triphosphate (GTP) (breaking down GTP causes changes of conformation in protein leading to inactivation or activation of G- protein) have enzymatic activity (can catalyze reactions) G-Proteins & Effector Proteins (have complex effects) o inactived effector – no influence on other proteins o activated effector – influence other proteins o converts neurotransmitter to intracellular chemical information (i.e. activation of effector enzymes/proteins (effector protein)) phosporylation of proteins o phosphorylation controls protein activity o protein ↔ protein – PO 4 ( protein kinase (add phosphate group) ↔ protein phosphotase(remove phosphate group) (inactivate ↔ active) Multiple sites can modulate enzyme activity o covalent modulation – chemical bonds formed e.g. adding phospate o allosteric modulation – changing shape (like chemical-gated channel) o NT receptor interactions are a from of allosteric modulation G-Proteins & Second Messengers o g-protein activates primary effector o primary effector generates a second messenger o second messenger activates second (downstream) Effectors cAMP system o cAMP serves as an intracellular (“second”) message for many effector proteins; “cAMP-dependent protein kinases” eg protein kinase A
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o G-Proteins can turn system “on” or “off” ie Gs vs Gi o note” same transmitter can act on Gs or Gi therefore effect depends on proteins expressed in post-synaptic cell. Effectors can modulate gene expression o downstream effector are transcription factors produces very long-term effects on neuron Amplification in 2 nd messenger pathways o transmitter activates receptor o receptor activates G-protein o g-protein stimulates adenylyl cyclase to convert ATP to cAMP o cAMP activates protein kinase A o protein kinase A phosporylates potassium channels G-Proteins and the shortcut pathway o Activated G-Protein modulates ion channel o indirect NT gating of ion channel o effects are via phosphorylation of channel; ie long-term gating IP 3 and DAG System o both IP3 and DAG serve as an intracellular messages for many effector proteins (“divergence” in system) o G-proteins can turn system “on” or “off” o all G-proteins are referred to as Go Chapter 5 Notes Electrical Synapses allow ionic current to pass equally well in both directions six connexin subunits comprise one connexon, two connexons comprise one gap juntion channel, and many gap junction channels comprise one gap junction.
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  • Fall '08
  • Kippin,T
  • Proteins, axon terminal

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