Class 11 Biology (India)
Correction to sodium-potassium pump video
Correction to "Sodium-potassium pump" video. Created by Sal Khan.
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- What is the name of the channel that K+ and N+ leak from?(3 votes)
- Sodium Potassium Pump uses ATP (topic of this video). This is not leaking.
Sodium channel or Potassium channel lets the ions leak through(3 votes)
- at university here in the UK, we were taught that the charge inside the neuron at resting state is -60mV compared to the outside the cell. Where in these videos it is said to be around -80mV at its "normal value". Can anyone explain this difference to me?(2 votes)
- I just read on-line that it is typically -70mV but can range from -40mV to -80mV. I'm sure it depends on many things, not least of which might be if you are looking at frog or human tissues. :-) I hope this helps.(5 votes)
- Did I understood this correctly?
- Potassium [K] pumps in the cell membrane and then goes back out because it is highly permeable?
- Sodium [Na] pumps out the cell membrane and it hardly goes back in because it is slightly permeable?(3 votes)
- Potassium tends to go out not because of permeability but because cell creates 'artificial' difference in concentrations. So K+ and Na+ ions tend to leave both locations in order to form an equilibrium.
And cell needs K+ and less Na+
that's why the pump has to work continuously.(1 vote)
- Hi in this video, it said that the Vm was -80Vm, but in the original video Mr. Sal created, he said the Vm was -70. So which is the real Vm.(2 votes)
- I believe that the difference is purely due to multiple sources finding different answers. 70Vm could be the value the a text book claims to be correct, and 80Vm could indeed be the value commonly found in the experiments at Penn medical school. Perhaps the cells of each finding responded differently due to the surrounding environment, or the solution they were tested in provided added extracellular charge. If both experiments followed correct accepted procedure, they could both be true :-)(1 vote)
- At about6:40Sal says that the greater flux of K thru the membrane is the main cause for the voltage difference, not the Na/K pump, But Professor Steven Baylor/Vaylor (sp?) at U of Penn, in his statement, says that the COMBINATION of these 2 things is the main cause.(2 votes)
- The pump doesn't work very quickly compared to leak channels in the cells. In a typical neuron, there are 20 K leak channels for every 1 Na leak channel. After an action potential goes through its phases, the voltage difference returns to rest primarily through leak channels because they are more numerous, quicker, and require no energy.(1 vote)
- When more than two potassium are pumped into the cell what will happen?(2 votes)
- First of all, nothing is pumped 'into the cell wall'.
Sodium/potassium pumps are explained on the example of human cells (meaning no cell walls) plus nothing is pumped into the cell wall or the cell membrane. It can be pumped only through the membrane or the wall.
In the case you succeed pushing more than two K+, you end up creating little mess and disrupting homeostasis in the cell.
On the other hand, it is hardly possible for the K+ to bind to the three places. Basically, there is no binding place on the pump for additional K+ ion.(1 vote)
- Please explain again why the inside is less positive than the outside. Also,does that mean that the inside is not negative it is just less positive than the outside? I do not understand what Sal meant in this video and the edits he made. If the outside is more positive then why would K+ ions from the inside of the cell membrane want to go to the outside through the channels? Wouldn't it be the other way around where ions from the outside want to come into the inside due to the gradient?(2 votes)
- I have been told by a teacher that if the extracellular K+ concentration is increased, then the resting membrane potential of the cell will become less negative (more positive), why is this?(2 votes)
- this should be because the resting membrane will accept the extracellular K+,incresing the amount of K+ inside the membrane.(1 vote)
- That doesn't make any sense. For the potassium to flow through the cell membrane AGAINST it's electrochemical gradient the channel should have to perform an active transportation of this potassium. But I understood this transport is a passive one. Is this right?(1 vote)
- Potassium flows through the membrane of a neuron through voltage-gated channels or leakage channels depending on when in the neuron's "life" we're considering. That is passive transport. The sodium-potassium PUMP uses ATP energy to restore the relative amounts of Na+ and K+ to reset the resting potential after the passing of an action potential - that part is ACTIVE and is the time when the ions are flowing AGAINST the gradient.(3 votes)
- the channels which permit K+ and Na+ to leak in are not voltage gated channels right?(1 vote)
- Correct, they are not. Ions (i.e., Na+, K+) traveling trough leak channels is a form of passive transport. It does not require any energy, or any particular conditions to open or close them - they are always open!(2 votes)
Two corrections I want to make to the video on the sodium potassium pump. One very minor one-- and I don't think it would trip too many of you guys up, but near the end of the video, as we learned, we have potassium getting pumped into the cell by the sodium potassium pump. Let me draw the membrane. It'll actually be useful in the more significant correction I'd like to make. So let me draw a cross section of a cell membrane. And let me draw the sodium potassium pump right here. We saw it pumps out three sodiums for every two potassiums that it pumps in. It definitely doesn't look like that, but it gives the idea. And we're pumping potassium ions in-- so K plus-- and we're pumping sodium ions out-- and that's what the whole point of that video was. When this thing changes shape with ATP, it pumps the sodium ions out. Now the minor correction I want to make-- and I don't think it would have tripped you up too much-- is near the end of that video, I drew the potassium ions-- and I wrote a K plus, but a few times near the end of the video, I referred to them as sodium ions-- and I don't want that to confuse you at all. It is potassium ions that are getting pumped in. Two potassium ions get pumped in for every three sodium ions that get pumped out. So I don't want-- even thought I drew a K plus, sometimes I said sodium by accident. Don't want that to confuse you. That is the minor error. The more significant error is that I said that the main reason that we had this potential difference-- why it is more positive on the outside than the inside-- so this is less positive. I said that the main reason was because of this ratio. We're pumping out three sodium ions for every two potassium ions that we pump in. And I just got a very nice letter from a professor of physiology, Steven Baylor at University of Pennsylvania, and he wrote a very interesting email and it corrects me. And it's a very interesting thing to think about in general. So here's what he wrote and let's think about what he's saying. He says: Here at Penn Medical School, we have a nice teaching program that stimulates the ion fluxes across a generic cell, --So the ion flux is just the movement of the ions across the membrane-- including that due to the sodium potassium pump and that which arises from the resting permeabilities of the membrane. So the resting permeabilities is how easy it is for these ions to go through the membrane. And we'll talk more about that in a second. And the resting permeabilities of the membrane to sodium, potassium, chloride, et cetera. One option our program gives students is to change the pump stoichiometry from three to two. So when he's talking about pump stoichiometry from three to two, he's just talking about they're changing the ratios. So they change it from 3:2 to 2:2. So what that means is, they have a simulation program that says, well, what if the sodium potassium pump, instead of pumping three sodiums out for every two potassium it pumps in, what if it was even? What if it was two sodiums and two potassiums? And based on my explanation of why we have this potential difference, that should not lead to a potential difference if the main reason was the stoichiometry-- the ratio of sodium being pumped to the potassium being pumped in. But he goes on to say: They could change it to 2:2 in the simulation. As a result of this maneuver, the membrane potential changes from its normal value of about -80 millivolts-- and they measure that. They take the voltage here minus the voltage there so that you get a negative number. This is more positive. It's a larger number. So it changes from -80 millivolts to about -78 millivolts. So what he's saying is, if you change this from three and two-- three sodiums for every two potassiums that get pumped in-- if you change that to 2:2, it actually doesn't change the potential that much. You still have a more positive environment outside than you have inside. So that leads to the question-- then why do we have the potential if the stoichiometry of this ratio is not the main cause? So it says, it changes a little bit. The potential difference becomes a little bit less. The cell swells a few percentage and then everything stabilizes. So then he goes on to write: So while it is true that the normal stoichiometry of the pump does have a slight negative influence on the membrane potential-- that's just the membrane potential, the voltage across the membrane-- the imbalance in the pump stoichiometry is not the main reason for the large negative membrane potential of the cell. Rather, the main-- let me underline this-- the main reason is the concentration gradients established by the pump in combination with the fact that the resting cell membrane is highly permeable to potassium and only slightly permeable to sodium. So we said in the last video-- or the first video on the sodium potassium pump-- we said there were channels that the sodium could go through and there's also channels that the potassium could go through. And now what he's saying is that the main cause of the potential difference isn't this ratio, it's the fact that the membrane is highly permeable to potassium. So this is very permeable. Potassium can get out if it wants to, much easier than it is for sodium to get in. So what that happens-- even if this was a 2:2 ratio-- it's actually a 3:2, but even if this was a 2:2 ratio, even though this environment is more positive, you're just more likely to have to potassium ions down here bump in just the right way to get across and get to the other side, go against its chemical gradient, right, because you have a higher concentration of potassium here than over here. So you're more likely to have a potassium bump in just the right way to get through this channel and get out-- than you are to have a sodium be able to go the opposite direction. And that's what makes this environment. So you have more potassium coming outside because of this permeability than sodium coming inside-- and that's the main cause of the potential difference between the outside and the inside. And so thank you, Steven Baylor, for that correction. Very interesting.