NAME_____________________________________________________________TA__________________ SEC____7.012 Problem Set 6 FRIDAY November 19, 2004Answers to this problem set must be inserted into the box outsideProblem sets will NOT be accepted late. Solutions will be posted on the web.Question 1a) Pictured below is a neuron obtained from your TA. Surprisingly, the microscopicstructure of your TA’s neuron mimics that of a generalized human neuron . Label theneuron components marked with arrows and draw an arrow along the axon to indicateimpulse direction of the route traveled by a nerve impulse.Figure by MIT OCW.MIT Biology Department7.012: Introductory Biology - Fall 2004Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette Gardel2Question 1 continuedb) In a neuron, where do the signals from the excitatory and inhibitory synapses getsummed up in the decision to fire an action potential? (Circle the correct one.)Cell Body Axon Hillock Myelin Sheath Nerve Terminal Synaptic Vesicle Synaptic CleftShown below is a plot of the membrane potential at a single point on an axon as a functionof time as an action potential travels down that axon.0 mVTime-70TimePointATimePointCTimePointDTimePointB3c) For each of the four time points indicated (A-D), fill in the following: the stage of theaction potential, the status of the sodium and potassium channels, and the ion fluxthrough each channel at the point along the axon where the potential is being measured.(For the potassium channels give the answers for the voltage-gated type.)Please use the terms provided. Time PointABCDStage of action potentialVoltage-gated Na+ Channelstatus(Open or Closed/Inactive)Voltage-gated K+ Channelstatus(Closed, Open)Na+ Flowthrough Na+ Channel(Into axon, Zero, Out of axon)K+ Flowthrough K+ Channel(Into axon, Zero, Out of axon)d) What role do the Na+/K+ ATP-driven pumps (present in neuronal cell membranes) playin maintaining the resting potential?e) Consider an experimental injection of a number of positive ions into the axonalcytoplasm of a neuron. Explain how the voltage-sensitive sodium (Na+) channels initiatean action potential in response to this injection.f) In many cells there are two types of potassium (K+) channels present in the axonalmembrane. What is the role of each type of K+ channel, with regard to the membranepotential?g) The voltage-sensitive sodium channel has an inactivated state, in which the channel isnot only closed, but also unable to open in response to depolarization. When does thechannel shift into this conformation? What effect does this have on the direction ofpropagation of the action potential?4Question 2A. You have some drugs that affect neurotransmission, and you wish to determine whatsteps they are likely to affect.In a Petri dish culture of neurons, you depolarize a pre-synaptic cell with an electrodeand you observe a resulting action potential in that pre-synaptic cell. This step is thesame regardless of whether drugs are added. However, the effect on the post-synapticcell varies.AdditionsWhat you see in post-synaptic cell...No drugYou see a slight depolarization in the post-synaptic cell followed byno action potential in the post-synaptic cell.Drug 1You see a large depolarization in the post-synaptic cell followed by anaction potential in the post-synaptic cellDrug 2You see no depolarization in the post-synaptic cell andno action potential in the post-synaptic cellc) For the following, complete the statement with the letter(s) from the list below.i) The effect of Drug 1 could be that the… ________ii) The effect of Drug 2 could be that the…________A.Neurotransmitter is inhibited from degradation.B.Neurotransmitter is degraded.C.Neurotransmitter's reuptake is accelerated.D.Neurotransmitter's reuptake is inhibited.E.Neurotransmitter's receptor is blocked.5Question 2, Part BYou are working in lab that studies the adrenaline response. Many athletes come to yourlab looking for a drug that will give them an extra kick-just like adrenaline. You knowthat adrenaline (a.k.a. epinephrine) works in the “flight or fight” response and that it cantrigger action potentials in cardiac muscle, but you need to learn more.a) You find out that epinephrine results in an overall increase in calcium ion levels withinthe cytoplasm of muscle cells. Given this fact, what do you think is required to restorethe cardiac muscle cell back to its resting state?b) What are three ways that neurotransmitter can be removed from the synapse?c) You find out that epinephrine is removed from the synapse by uptake by the axon.With this knowledge, how could you design a drug to give the athletes the extra kick theyare looking for? How would it work?d) What possible side effects would this drug cause?6Question 3a) You receive a letter in the mail from ACDC (Americans for Cloning Dead Celebrities),asking for a $10 donation to support the cloning of a famous movie star, Goldie Starlet,who died in a plane crash in 1994 and no remains of her were found. Your friend, who is ahuge fan of Goldie, sees the letter and promptly whips out $10 to send to ACDC. Do youthink your friend made a wise decision? Explain your answer.b) A few months later, you watch a documentary on organ transplants, where a womannamed Rosie claims to have received Goldie’s left kidney during a kidney transplant in1993. Briefly outline the steps by which Goldie could be cloned with the help of Rosie.c) ACDC clones Goldie with some assistance from Rosie. However, the clone has a shortstature (typical of a known mitochondrially inherited disorder), whereas Goldie was muchtaller. Is Rosie a fraud or could there be another explanation?d) The ACDC finds out that Goldie had some of her eggs frozen in a fertilization clinic.Could the nucleus of one of these unfertilized eggs be used to clone Goldie Starlet? Whyor why not?e) Your friend thinks that ACDC should give Rosie a second chance. What steps could onetake so that this time the clone has the same stature as Goldie’s?f) After including your suggestions from part e), can you feel confident that the clonewill be 100% identical to Goldie in every way. Explain your answer.7Question 4Divya finds a new brightly colored mammalian species, which he names Magnificus colores. She isolates blueand green cells from different parts of this organism, and cultures each cell individually.a) Are the blue cells stem cells? Why or why not?b) Given that the green cell is a
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