sample_midterm_1_2006_key

sample_midterm_1_2006_key - YOUR NAME_ Student ID#_ MIDTERM...

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YOUR NAME__________________________ Student ID#_________________ 1 NPB 100 MIDTERM 1 SPRING, 2006 Your signature______________________ Question Score Total 1 20 2 12 3 7 4 5 5 16 6 6 7 20 8 10 9 4 TOTAL 100
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YOUR NAME__________________________ Student ID#_________________ 2 Question 1. (20 points) You clone the cDNA for a novel ligand-gated channel that is selective for cations. You construct the following hydrophobicity plot based on the predicted amino acid sequence. Hydrophobicity index N Amino Acids COOH H 2 12 3 A. (2 points) Is the amino terminus of this molecule extracellular or intracellular? intracellular B. (2 points) Is the carboxy terminus of this molecule extracellular or intracellular? intracellular C. (2 points) How many membrane spanning regions are there? 4 D. (3 points) Could the neurotransmitter binding site be located in region 2 of the molecule? Yes E. (4 points) Why or why not? Region 2 is extracellular. F. (3 points) Which region of the molecule (region 1, region 2, or region 3) is likely to have an excess of negatively charged amino acids? Region 3. G. (4 points) What is the purpose of these negatively charged amino acids? To concentrate cations in the vestibule, helping them to enter the pore. GO ON TO NEXT PAGE!
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YOUR NAME__________________________ Student ID#_________________ 3 Question 2. (12 points) You are studying a neuron that is in every way a typical neuron, except that it does not have any voltage gated potassium channels. In what ways will this neuron’s action potential differ from a normal neuron’s action potential? Explain the causes of the differences. 1) The peak of the action potential will be more positive, because there is no outward current through voltage gated potassium channels to bring it down (it still won’t reach the sodium equilibrium potential because potassium leak channels are open). 2) The depolarizing phase of the action potential will last longer, because there is no outward current through voltage gated potassium channels to repolarize the cell quickly (note that the cell does still repolarize as voltage gated sodium channels inactivate and the potassium leak current brings the membrane potential back to the resting membrane potential)
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sample_midterm_1_2006_key - YOUR NAME_ Student ID#_ MIDTERM...

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