Problem Set 4 Q&A - Problem Set 4 Cellular Neurobiology...

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Problem Set 4 Cellular Neurobiology Fall 2008 1. Vesicular trafficking is a complex process. a) Name the six steps of complete vesicular trafficking in order and give a brief description. Mobilization: loaded vesicle buds off an endosome and is free to move Docking: vesicle docks with protein complex on the cell membrane of the synaptic cleft Fusion: vesicle fuses with membrane, emptying its contents into the cleft Retrieval: protein complex pulls the vesicle out of the membrane (dynamins) Uncoating: vesicle sheds protein coat Reloading: vesicle fuses with endosome and is loaded with new transmitter b) How do action potentials that arrive at the terminal bouton trigger release and which step do they affect? Explain the mechanism. APs are the signal that triggesr SV fusion with the plasma membrane. AP depolarization of the terminal opens voltage-sensitive Ca++ channels, allowing a brief influx of Ca++ that binds to docking proteins (synaptotagmins). Conformational changes of the associated SNARE proteins (SNARE-PINs) acutely mediate vesicle fusion. c) What protein complex is involved in this step? Name 4 major components. SNARE complex; synaptobrevin, synaptotagmin, syntaxin, SNAP-25 2. Electrical synapses are an important, if understudied component, of cellular communication. What is another name for these special cell-cell contacts? Gap junctions a) Why would an animal have electrical synapses to some motor neurons? Give a famous example. Squid have gap junctions to some motor neurons so that some signals from the central nervous system reach muscles more quickly, allowing the squid to escape from danger. b) List five major differences between chemical synapses and gap junctions
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Smaller space between pre and post synaptic contacts Contains a gap spanning pore Rapid AP propagation May be non-rectifying or rectifying Allows passage of ions and small molecules directly between neurons Other answers possible c) In mammals, what protein forms the electrical junction pore? Describe its
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