2008 Exam 2 with answers

2008 Exam 2 with answers - BMB/MICRB 460 / March 6, 2008...

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BMB/MICRB 460 / March 6, 2008 NAME: Exam 2 / TEST FORM A TEST DIRECTIONS: RECORD a single answer for each multiple-choice question on the line to the left of the question. Write your answer to the short answer questions LEGIBLY in the space provided Questions are worth 4 points unless marked otherwise. I will post the exam, answers and scores as soon as all students have taken the exam and grading is complete. 1. (6 pts) An action potential occurs when the membrane depolarizes to –40 mV (see figure below). Use words or pictures to compare the effect on membrane potential that you would expect if you increase the permeability of the membrane to potassium (K+) versus increasing the permeability to sodium (Na+). Concentration of Na+ is higher outside the cell than inside. Concentration of K+ is higher inside the cell than outside. Therefore, when membrane becomes permeable to Na+ due to opening of sodium channel, sodium will flow into the cell, membrane is depolarized and an action potential will result. When the membrane becomes permeable to K+ due to opening of K+ channel, K+ will flow into the cell, the membrane is depolarized and an action potential will result. 2. (6 pts) Draw, diagram or explain WHY and HOW activation of the Muscarinic Acetylcholine receptor and the Nicotinic Acetylcholine receptor lead to opposite polarization responses. You may want to refer to your answer above. M-Ach receptor is a G protein linked receptor. Binding of Ach to the M-Ach Receptor causes trimeric G protein to associate with the receptor and alpha subunit exchanges GDP for GTP. Alpha subunit dissociates from the beta/gamma subunits and the beta/gamma complex then acts to open a K channel leading to hyperpolarization of the sinoatrial node and a slowing of the heart beat. N-Ach is an ion-channel receptor. Binding of Ach to the receptor causes a change in conformation of the receptor, opening the receptor-intrinsic Na+ channel. Na+ flows in and the membrane is depolarized leading to a muscle contraction.
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Form A NAME:_______________________________________ 2 3. (6 pts) Draw, diagram or describe a method to test if two proteins interact DIRECTLY. Include discussion of the source of your proteins for the experiment. One possible answer (other permutations of this answer may be acceptable) Purify the two proteins. Make a hisX6 fusion to protein A and a glutathione S transferase (GST) fusion to protein B (important that you use different tags). Separately express each in bacteria and then purify the fusion proteins from bacterial cell lysates using Ni-coated beads for His-A and glutathione–coated beads for GST-B. After you have pure preparations of His-A and GST-B. Mix them together to allow binding to occur if possible and then pull down one of the two fusions. For example, pull down His-A with a Ni-coated bead. Run the bound material on an SDS gel and then analyze the gel for the presence of the GST-B fusion protein by immunoblotting with an antibody to A or an antibody to GST. Do the proper controls
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2008 Exam 2 with answers - BMB/MICRB 460 / March 6, 2008...

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