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MCB136,FaII 2023

Practice Set 2 (ps2)

5 points

Due 48 hours after your discussion section

Instructions: pIease Read AII CarefuIIy

. This is a timed practice set. You will have 48 hours to complete the Practice set; however,

we expect that you will be able to complete these problems in 1一3 hours.

. This Practice set is designed to mimic a typical midterm exam. All of the questions are taken from previous years， midterm exams or graded problem sets. Problems earn points based on effort. Blank or irrelevant answers, or those that reflect a lack of effort, will not earn points.

. Carefully read through each question before you start working on the PRACTICE sET.

. This is an open note/book problem set. You may consult online resources, lecture notes, required content and optional reading. You may discuss the problems in your study groups and in discussion sections; however, you must submit your own independent answers.

. Your answers must be written within the box provided. AND

your uploaded Ps must match the template* 一 questions and answers must be on the same page, in the same place. You can type an answer using 12-point font into the

PDF fields. or you can print the problem set and write in your answers using clear handwriting that is no smaller than the problem set font. Illegible answers and information written outside the box (or not on the blank) will not be graded.

*practice sets not matching the template might lose points as a result

. You must convert your practice set to a pdf and submit via gradescope with "Your Name一ps2" as the filename.

. To be eIigibIe for fuII points, the compIeted practice set must be submitted no Iater than 48-hours after your discussion section. Assignments submitted after that time will be eligible for half credit.

. Honorstatement: I swearon my honor that:

-l have read all of the instructions.

-l will turn in my own original work.

-l understand that this assignment maybe validated for originality via Turnitin according to Uc policies:

h:ttps ://dls.berkeley.edu/services/academic-integrity/turnitin-instructors-getting- started/ turnitin-policies

. l will not share this problem set with anyone outside my discussion section.

1. using a VoItage-cIamp experiment, you find that appIying a new pIant compound to a neuron eIicits the currents dispIayed beIow. whiIe the pIant compound is appIied to the neuron, you change the membrane potentiaI to the vaIues indicated on the graph (in mv), and them measure the resuIting current.

A. Draw the IV CurVe for the ion channeI in the experiment above. You may use the axes at right or uPIoad an image of your graPh beIow.

CIearIy IabeI the graph and axes (0.5 pt).

B. Based on the information above, hypothesize what type of ion channeI is opened by the compound. BriefIy expIain the reasoning behind your answer and Iist aII assumptions (0.25 pt).

A voltage-gated cation channel, such as a voltage-gated sodium channel or a voltage-gated calcium channel, is likely the cause of the observed lv curve's increase in current with depolarization.

Reasoning: Depolarization causes voltage-gated cation channels to open, allowing the low of cations (positively charged ions) like calcium (ca2+) or sodium (Na+).

C. Design an experiment and state one resuIt that WouId determine Whether your hypothesis is correct.（0.25 pt).

we can prepare the neuron in the same circumstances as the initial experiment, applying the plant chemical as necessary.

Apply a speciic ion channel blocker (such as tetrodotoxin for sodium channels or nifedipine for calcium channels) to the predicted channel.

Repeat the voltage-clamp experiment, adding the ion channel blocker, and measuring the current that

results at various membrane potentials while the chemical is applied. The blocker should greatly lower or completely prevent the observed increase in current as the membrane potential is changed, assuming the hypothesis is right and the chemical opens voltage-gated cation channels.

2. You are performing experiments on a temperature-sensitive neuron isoIated from a CoId- sensing organ that has never before been studied. using a voItmeter, you find that appIying CoId stimuIi to this neuron triggers depoIarization under the foIIowing Conditions:

	concentration (OUT)	concentration (IN)	Ion permeabiIity at rest
Na+	75. mM	100. mM	10.
K+	10. mM	150 mM	1.0
ca2+	0.2 mM	2.0 mM	0
cl-	10. mM	10. mM	5.0
RT/F=26.7

A. caIcuIate the resting potentiaI of this neuron. Set up the correct equation and show your work. (0.5 pts)

B. caICuIate Ek,ENa, ECa and ECI- . Set up eaCh equation and show your work. (1 pt)

Ek+

ENa+

Ecl-

ECa2+

C. Based on this information, hypothesize what type of ion channeI is opened by coId in this neuron. (seIect one; 0.25 pt).

sodium channel

0 potassium channel

0 chloride channel

0 calcium channel

0 Non-selective cation channel

D. BriefIY expIain the reasoning behind Your answer (1-2 sentences). (0.5 pts)

The equilibrium potential for sodium ions (ENA+)，which is closest to the resting membrane potential (EK+)，is -7.58 mv based on the information provided. This shows that when a

is at rest，sodium ions (Na+) have the strongest driving force to enter the cell.

E. You performed VoItage-cIamp recordings from these newIY identified coId-sensitiVe neurons. Your resuIts are schematized beIow. Answer the foIIowing questions based soIeIY on this information.

E1. Based on the resuIts in 2E OnIY, was your ion channeI hypothesis (frOm 2c) correct?

So it seems sense to speculate that exposure to cold may cause sodium

channels (Sodium channels) in this neuron to open，allowing sodium ions to

enter the cell and possibly causing depolarization and altered neuronal activity in response to cold stimuli.

E2. List an essentiaI ControI in this experiment and why it is neCessary to interpret the resuIts? (0.25 pts)

A "Negative control" or "Baseline control" in which the identical voltage-clamp recordings made on the neurons without the introduction of the novel plant chemical or cold

crucial control in this experiment. lt assists in determining if the measured currents and in response are indeed caused by the action of the plant chemical or the cold shocK and a product of random luctuations or other variables.

3.You identify a new cone snaiI species that paraIyzes its prey. You hypothesize that the cone snaiI Venom contains a toxin that changes action potentiaI firing in the prey,s neurons.

To test this hypothesis, you measure the membrane potentiaI from a neuron under physioIogicaI ion concentrations.