midterm+1+key - Biology 350 Name_ Midterm 1 (print full...

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Biology 350 Name__________________________ Midterm 1 ( print full name) Total points 100 1- (25 points) The recording set-up below represents a neuromuscular junction, the synapse of which is mediated by acetylcholine and a ligand-gated postsynaptic receptor channel. Under normal conditions after stimulation you record the changes in postsynaptic membrane potential shown below: Recording A motor neuron axon (a) The concentration of Ca 2+ outside the axon is 1 mM and inside the axon is 0.1 mM. What is the equilibrium potential of Ca 2+ ? Show your work. Log 0.1 = -1 Log 1 = 0 Log 10 = 1 E Ca = (0.058/2) * log [(1)/(0.1)]= 29 mV ( 5 points ) (b) Based on the potential calculated in (a), in what direction (inward or outward current) will Ca 2+ flow through the presynaptic membrane when you stimulate? Inward. ( 2 points ) What will be the consequence of this Ca 2+ flow at the axonal terminal? The presynaptic vesicles will fuse to the presynaptic membrane and the neurotransmitter (acetylcholine) will be released. ( 3 points ) (c) Now you bathe the tissues in the diagram in a Ca 2+ -free solution, how will Recording A change and why? There will be neither postsynaptic depolarization nor action potentials recorded because without Ca 2+ in the solution Ca 2+ will not flow into the presynaptic membrane and no neurotransmitter (acetylcholine) will be released. ( 5 points ) 1
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Biology 350 Name__________________________ Midterm 1 ( print full name) Total points 100 You isolate two different toxins (toxin X and Y) from a plant and you test them in the same experimental conditions as in Recoding A stimulating presynaptically. For each one of the toxins you record the responses shown below. On which channel does each toxin act. Note: In both cases (d and e) you know that acetylcholine is indeed released during stimulation. Explain your reasoning . (d) Toxin X Toxin X blocks voltage-gated Na + channels because despite the fact that we record a postsynaptic depolarization we do not record action potentials. The toxin is similar to TTX. ( 5 points ) (e) Toxin Y Toxin Y blocks the acetylcholine channels because despite the fact that acetylcholine is realesed during stimulation we record neither a postsynaptic depolarization nor action potentials. The toxin is similar to curare. ( 5 points ) _______________________________________________________________________ _ Do not write below this line 2
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Biology 350 Name__________________________ Midterm 1 ( print full name) Total points 100 2- (15 points) The receptor shown below is an olfactory receptor specific to ethanol. After applying a brief stimulus (a puff of ethanol) you record the response shown on
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This note was uploaded on 04/15/2008 for the course BIO 350 taught by Professor Unsure during the Fall '07 term at University of Washington.

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midterm+1+key - Biology 350 Name_ Midterm 1 (print full...

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