NROS 307 quizzes with complete solutions

what is the formula for resistors in series vs in parallel in series: add R= R1 +R2.. in parallel: 1/R= 1/R1+ 1/R2... What is Ohm's law equation? V=IR Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:02 / 0:15 Full screen Brainpower Read More what is the formula for capacitors in series vs in parallel in series: 1/C = 1/C1 + 1/C2.. in parallel= C= C1 +C2.. what kind of molecules can pass the cell membrane lipid bilayer most easily? Which have the hardest time diffusing through? small hydrophobic molecules small uncharged polar molecules large uncharged polar molecules charged molecules (ions) where does capacitance come from in the cell? the lipid bilayer: proteins, ion transporters does adding more membrane layers increase or decrease capacitance? decrease what components of the membrane are responsible for resistance? the ion channels What is the hydrophobic effect? The exclusion of non polar substances from an aqueous solution. Nonpolar molecules aggregate to avoid contact with hydrophilic molecules, particularly water. -polar molecules are more attracted to the dipoles of each other than non polar and thus exclude the non polar molecules (makes them arrange in a specific manner) what is the physical basis for the hydrophobic effect? the second law of thermodynamics: ENTROPY of a system wants to increase (occurs when water molecules interact with each other and exclude the non polar molecules) order the following molecules with respect to their ability to cross a membrane: glucose, water, NO, Na+, ETOH, RNA NO, ETOH, water, glucose, Na+, RNA what are the 2 factors that determine whether a molecule can cross a membrane? which one is more important? 1) charge (polarity) 2) size what are the 3 basic membrane transport protein types? which are faster compared to the other? 1) ATP powered pumps 2) Ion channels (either open or closed and allow ions to flow down their M gradients) 3) Transporters -generally 1 and 2 are faster than 3 what are the 3 types of membrane transporters 1) uniporter: only 1 molecule in 1 direction 2) symporter: 2 molecules in the same direction 3) antiporter: 2 molecules in opposite directions for symporters/antiporters, what kind of transport are they/ what supplies the energy in both, 1 molecule moves down its M gradient, which supplies the energy needed to transport the other molecule against its gradient -both passive and active think about the graph plotting initial rate of uptake and concentration? which is fastest/ slowest? fastest= diffusion ion channels transporters slowest= ion pumps why do molecules tend to move down their M gradients? Due to Brownian Motion: the random movement of particles in solution; there is a greater probability that molecules will be pushed into the area with less collisions/resistance from other particles is there osmotic pressure present is the membrane is impermeable? No, there is no osmotic pressure since the particles cannot cross each membrane what is the simplified nernst equation to know? E ion= 58/z log (Co/Ci) What is the Nernst potential? the potential across a cell where the electrical and chemical gradients are exactly equal and opposite so that there is no net flow of ions does every cell have a membrane potential? If so where does it come from? Yes, every cell has a membrane potential -comes from mainly the inside of the cell (houses the negatively charged proteins/RNA) what would the membrane potential of a cell be if only specific ion channels such as Na+ or Cl- channels were open? -quiz 2 the potential would be equal to that specific ions nernst potential (e ion) quiz 3 start How do you determine if an ion will flow into or out of a cell at the following voltage potentials? -100mV, -76mV, 0mv, +68mV, +100mV - K+ nernst potential= -75mV -Na+=+68mV -Ca 2+= +46mV if the voltage is more negative than the nernst potential (of ions for positive charges), then the ion will flow into the cell what will the flow be like in or out of the cell at that specific ions nernst potential? there will be no net flow How do you determine if an ion will flow into or out of a cell at the following voltage potentials? -100mV, -76mV, 0mv, +68mV, +100mV -for a negative charged ion Cl- nernst potential= -100mV if the potential is more positive than its nernst potential the ion will flow into the cell If the nernst potential of Na+ is +50mV (ENa+), explain why more Na+ will flow through open sodium channels if the cell membrane potential is at +10mV than if the potential is at +40mV since 10mV is farther away from +50mV, at this potential there will be a stronger driving force than there will be at +40mV. Thus, at +10mV, more sodium will be flowing into the cell due to driving force what 2 things does driving force involve? what is the formula for driving force? the number of open channels as well as the difference between the membrane potential and the nernst potential of a specific ion I ion= g ion x (Vm -Eion) what factors go into determining the resting membrane potential of a cell? there is a "tug of war" that exists between ions -factors= 1) conductance of ions 2) nernst potential of the ions 3) how permeable the ions are through the membrane (how many channels are open) what will the resting potential of a cell be if there are equal conductances of Na and K? it will be an average of the 2 nernst potentials What is the modified Goldman Equation? explain the concept and what factors go into determining it. What ions is it dependent on? what is the actual equation the goldman equation gives the Vm ( the equilibrium membrane potential) -dependent on Na, K, and Cl (ENa xgNa)+(EK xgK)+(ECl x gCl)/ gNa +gK +gCl Refer to the graph relating resting membrane potential and K+ concentration out of the cell 1) why are the 2 curves slightly different? 2) why are they almost the same at higher K+ concentrations 1) the 2 curves are different because Na+ is also involved, not just K+ 2) the lines are dependent on the driving forces for both Na and K. E Na= +58mV and EK= -75mV As the membrane potential becomes more negative, the driving force of Na increases, which also causes the EK to increase, but overall Na wins out over K what are the 2 types of potentials and what is the difference between them? electrotonic potential: local and completely passive, due to the diffusion of charges that causes changes in the voltage (aka membrane current), type of graded potential, the potential tends to dissipate over time (becomes weaker with distance) action potential: active (involves channels opening/closing), triggered by an electrotonic spread, covers longer distances, not local/graded what is the purpose of the action potential? to transmit information over long distances as quickly as possible without losing any of the information sent what is voltage clamping and what does it measure? voltage clamping controls the voltage across a membrane and holds it at a particular value -measures the ion current flow to determine the size of the depolarization (small or large) what 2 main ions determine the current in voltage clamping? what kind of depolarizations/currents do they make Na and K -Na makes a negative depolarization (inward current), K makes a positive one (outward current) How do you test the idea that changes in Na+ and K+ permeability underlie the action potential? block either the Na or K channels using specific drugs what drug blocks voltage gated Na channels, which drug blocks voltage gated K channels TTX blocks Na, curve would disappear TEA blocks K, curve would disappear what would happen if the voltage was clamped at the Nernst potential for Na+ in terms of Na and K Na current will remain at 0 (no driving force exists/no net flow) -K current will increase dramatically (large driving force) where is the positive feedback loop located in an action potential? when sodium enters the cell; as potential increases towards E Na, the probability of ion channels opening increases and the + feedback loop kicks in at the threshold level -higher voltage= greater probability of channels opening where is the negative feedback loop located in an action potential? when K leaves the cell/ the voltage gated K channels themselves because they tend to turn themselves off automatically what is considered to be a leaky channel? all the ions/flux that normally occur at rest (want to bring potential back to resting potential) in what fashion do individual voltage gated channels tend to open? all or none fashion- similar to the action potential what would you expect from a patch clamp recording of the following: 1) VG Na channel in squid 2) VG K channel in squid 3) VG K channel in mouse 1) inward current 2) outward current 3) outward current (but shorter than in squid since the channels in a mouse can inactivate when they see fit) what properties are necessary for a protein to act as an ion channel? the protein must be hydrophilic enough to interact with the ion itself and be non polar to be stable in the membrane most amino acids in an ion channel chain are what? -how many transmembrane proteins are needed to create a pore for ions to flow through hydrophobic (stable in the membrane) and do not have space in/bt -multiple transmembrane proteins why do voltage gated ion channels in patch clamp recordings open to the same amplitude each time? bc the driving force is maintained at the same level each time How can both proteins have similar functions? the proteins have multiple subunits -one can have more variability than the other so the shape of the AP can be changed while the protein function is still similar compare the structures of the Na and K subunits? Na subunit= less variability so more consistency in terms of the Na channels -called pseudosubunit K subunit= more variability in orientation possibilities which allows different AP shapes -true subunit How can a channel distinguish between different ions? Ion channels have selectivity filters -in the channel, the carbonyls present knock off water from the ion going through the channel -however, the carbonyls cannot appropriately knock of and dehydrate the ion unless the channel is attuned to the specific crystal radius of the ion itself -thus, if the distance is not specified to fit the crystal radius of the ion going through the channel, the ion will not be able to move through the channel (specificity to ions) Which ion is better at dragging along water: Na or K Na is better (larger hydrated radius) than K bc even though K+ is a bigger ion overall, Na+ is smaller and is able to distribute its positive charge over a larger SA than K+ -this larger SA of positive charge attracts more water molecules overall: smaller ion size= greater charge distribution and greater hydrated radius -however, higher hydrated radius= less mobility (water slows it down) How can an ion channel sense voltage? an ion channel can sense voltage changes due to the presence of certain +/- charges that create movements in the S4 region both +/- charges are stabilized in the TM domain, and - charges are present in the membrane -if the negative charges decrease (membrane depolarizes) then the overall protein is less stable and more reactive (the structure will rotate and move out of the membrane in order to become more stable) -overall, the protein channel is sensitive to voltage and will change configuration (open or closed) depending on voltage changes -referred to as the "digital switch" does more +charge or more -charge cause the protein channel to favor the open configuration? more + charge what happens if K channels open first in an AP? Vm would go down and compete/short circuit the + feedback loop (due to Na) what is threshold? where the + feedback loop kicks in and the probability of Na channels opening increases dramatically How can you use patch clamp analysis to prove a certain voltage is a K+ or Na+ voltage gated ion channel? show the reversal potential (= to nernst potential if only 1 ion type) what exactly determines what the nernst potential of a specific ion is? the relative conductance of ions Compare and contrast the Na voltage gated channels with the K voltage gated channels in terms of their subunits Na subunits= 4 total, allow the channel to open much more quickly than K channels since the subunits are much closer together *** allows for Na channel consistency How is channel inactivation achieved? through the S4 domain moving up and the ball and chain mechanism blocking the ion channel passage -at rest s4 domain is down in position - absolute refractory period= the time it takes for the ball to move out of the way of the ion channel does inactivation occur at the same time or different times for each ion? different times for each ion -can be based on probability what are the functions of inactivation? 1) stops the + feedback loop 2) prevents the AP from going backwards Draw out the APs you'd expect for the 2 different types of K+ channels? 1) being where the whole channel inactivates 2) where the whole channel does not inactivate 1) same basic AP curve, except a much shorter and smaller hyper polarization stage since it can fire another AP more quickly 2) "normal AP"- bugger hyper polarization stage Some vertebrate K+ channels inactivate, how would you expect these channels to inactivate and how would you test it? remove the ball from the K voltage channel chain why does the size of currents change depending on the voltage held before the depolarizing trigger voltage occurs? there are different numbers of ion channels available at different voltages -the greater number of channels available leads to a greater size in the current **proves that the opening of ion channels is probabilistic where does the inward current actually come from? what is its "formula"? the probability of S4 domains opening X the # of voltage gated Na channels available define threshold in terms of ion currents and in terms of molecular biology what is the combined definition ion currents: when the inward current overcomes the outward current and triggers the advent of the positive feedback loop molecular biology: the probability of s4 domains to detect a change in current combined definition: voltage where the s4 domains open and trigger voltage gated Na channels to open which cause the inward current to exceed the outward current and triggers the positive feedback loop what is the combined definition of threshold? The voltage where the probability of S4 domain movement applied to the population of available voltage gated Na+ channels causes an inward current that is greater than the outward current and triggers positive feedback Is threshold at the same membrane potential at all parts of the cell? no, the threshold is different in different parts of the cell since there are different amounts of ion channels open what is the axon hillock? the part of the neuron with a high M of ion channels where the membrane potential dips down what would threshold be like for a myelinated neuron? how could the threshold be changed? it would be alternating between high and low threshold -can be changed depending on the number of open Na/K channels can there be back propagating action potentials? yes, AP's can travel back to the dendrites depending on the number of ion channels present what is the relationship between current strength and distance the change in membrane potential decreases with distance -fades logarithmically what kinds of resistance do you want for a long distance depolarization? what about a short distance depolarization? long= high Rm and low Ra -Rm= membrane resistance, Ra= axial resistance short= low Rm and high Ra what is the formula relating voltage change to the length constant/ position? what is the general formula for determining the voltage at x=lambda Vx= Vo e^-x/lambda V=Vo/e e=2.7 =approximately 37% of the max value of Vo what is the formula for determining the length constant lambda? SQ ROOT of Rm/Ra -units= cm describe the concept behind the length constant equation in words? the distance from the initial voltage event for the voltage to fall to 37% of its original value what is the formula for determining the V during a depolarization current through a parallel RC pathway? V=iR (1-e^-t/TAU) where t= time from the beginning of the pulse and TAU (time constant)= RmC what is the meaning of the time constant and what is its equation? Tau= RmC -time for the V to rise to 63% of its final value Suppose you penetrate a spherical neuron with current injection and voltage recording electrodes. The cell is 60 μm in diameter and has a resting membrane potential of -60mV. You inject a square pulses of hyper-polarizing current into this cell and obtain the following voltage and current records: current= 5nA A) estimate the time constant TAU of this cell B) what is the cells input resistance and capacitance A) 40 * .63= 25.2 initial voltage plus change= 60+ 25.2= 85.2 time at voltage of 85.2= approximately 40 msec B) resistance V=IR R= 40/5= 8ohms capacitance= Tau= RmC C= 40/60= .667 F Add or remove terms Choose a