Emma Chesley Collaborators Raoul Khouri Question 1 3 points Fall 2014 7 012 Problem Set 7320 Points total DUE Friday 12 05 2014 AT 9 45AM ONLINE When an individual is exposed to an infectious agent the immune system responds by producing soluble antibodies specific for that infectious agent Assume that you have three different viruses Viruses A B and C Virus A and Virus C have different capsid proteins but the surface of each capsid protein has an identical stretch of 40 amino acids Virus A and Virus B have completely different capsid proteins but Virus A and Virus B have a 100 base3pair region of DNA that is identical Virus B and Virus C have nothing in common You expose individual 1 to Virus A and measure the following response Note f o r e b m u N f o g o L c i f i c e p s s e i d o b i t n a Days You expose individual 2 to Virus A and measure the following response s e i d o b i t n a c i f i c e p s f o r e b m u N f o g o L Days For each of the following conditions indicate if that condition could result in the increased response seen in individual 2 In each case where the conditions could result in the increased response explain how that condition caused the increased response Condition Yes or No If yes explain how that condition caused the Individual 2 was previously exposed to Virus A Individual 2 has more immature B cells Individual 2 was previously exposed to Virus B Individual 2 was previously exposed to Virus C Yes No No Yes increased response The increased response is due to the fact that the individual will have more mature B cells that can produce the antibody to ght off the virus The increased response is due to the fact that the antigen that is recognized on the capsid of virus C may be the same amino acid sequence as virus A This means that the mature B cells can create antibodies to ght off virus A Question 2 6 5 points The following four distinct protein complexes are found in the plasma membrane of nerve cells Each is required for the normal function of the nerve cell Resting K channel Voltage3gated Na channel Na K Pump Voltage3gated K channel a A nerve cell has a resting membrane potential of approximately 370 mV Below list which protein complex or complexes are essential in establishing the resting membrane potential Also for each protein complex you list include what ion s move through that protein complex and in what direction that ion moves into the cell or out of the cell to form the resting membrane potential Direction of ion movement Protein complexes Ion s moved Resting K Channel K K goes out the the nerve cell Na K Pump Na K Na goes out of the nerve cell and K goes into the cell b A nerve cell can fire an action potential Below list which protein complex or complexes are essential to generate an action potential Also for each protein complex you list include what ion s move through that protein complex and in what direction that ion moves into the cell or out of the cell to generate an action potential Direction of ion movement Ion s moved Protein complexes Voltage gated K Channel K K goes out of the nerve cell Voltage gated Na Channel Na Na goes into the nerve cell c Voltage3gated Na channels have three states open closed and inactivated These channels adopt the inactivated state for a brief period of time right after they have just been open Label the following diagram of a neuron in which an action potential is occurring at the place marked with a star in the following ways 33 Mark the place where an action potential just occurred with an X 33 Circle one place where an action potential would occur next 1 2 3 4 d At each location in the diagram above 134 indicate whether the voltage gated Na channels found there would be open closed or inactivated 1 Closed 2 Closed 3 Open 4 Inactive Below is shown a normal action potential in a nerve cell e The following compounds alter the action potential by interfering with one of the protein complexes listed above For each compound describe how one of the protein complexes above can malfunction to generate the specific action potential This compound may affect the voltage gated K channel This would happen if the channel is not working the gradient cannot enter the depolarization phase so the action potential would not re 50mV 70mV 50mV Compound A 70mV This compound may affect the voltage gated Na channel This would happen if the voltage gated Na channel isn t working and so the gradient cannot enter the depolarization phase so the action potential would not re 50mV Compound B Question 3 4 5 points 70mV Bungarotoxin causes accid paralysis because it binds to the acetylcholine receptor thus stopping acetylcholine from binding to the receptor thus causing it to activate Bungarotoxin causes rigid paralysis because it causes the release of vesicles that contain neurotransmitters to be released at an uncontrolled rate They bind to the acetylcholine receptor causing it to activate at an uncontrolled rate a Both 3bungarotoxin and 3bungarotoxin affect signaling at the neuromuscular synapse 3bungarotoxin irreversibly binds to the acetylcholine receptor but does not activate it 3bungarotoxin binds to cellular proteins and stimulates release of vesicles One of these toxins results in rigid paralysis where the muscles contract but do not relax The other toxin results in flaccid paralysis where the muscles fail to contract Which of these toxins results in rigid paralysis Explain your answer b Glutamate is the major excitatory neurotransmitter in the central nervous system brain and spinal cord acting through AMPA and NMDA receptors i What is the general role of Ca2 channels at the synapse Explain ii Does an increase in Ca2 influx increase decrease or not change AMPA and NMDA receptor activation at glutamate3regulated synapses Explain The increase in Ca2 in ux causes an increased amount of glutamate secretion thus increasing the AMPA and NMDA receptor activation Its general role is to be the nal voltage gated channel on the axon When the Ca2 ions enter the nerve cell they cause the neurotransmitters to be secreted from the end of the axon Conantokin3G is a potent venom isolated from the fish3hunting cone snail It is a competitive inhibitor of the NMDA receptor iii Would application of conantokin3G increase decrease or not change the likelihood of an action potential in the postsynaptic cell Explain The threshold potential is normally 50mV After conantokin3G iv application would the threshold potential be higher lower or
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