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Video transcript

what I hope to do in this video is give ourselves an appreciation for the sodium potassium pump and as the name implies it pumps sodium and potassium but it does it in different directions so this little depiction right over here this is the my drawing my rendition of the sodium potassium pump it's a trans membrane you can say protein complex right over here and in this resting state it is open to the inside of the cell and it has a fin it has an affinity for sodium ions and so the sodium ions you see three sodium ions depicted here in blue they're going to bind to the pump and once they bind to it then it's going to be it's going to want to be phosphorylated by an ATP and we see that right over here this is ATP ad en si adenosine triphosphate and when it gets phosphorylated it's a release of energy and it allows the conformation of the actual protein to change so the new conformation of the protein it's now going to open up to the outside closed off to the inside and now it's no longer going to have an affinity for sodium ions but an affinity for potassium ions and this is fascinating that release of energy change of conformation that these proteins really are these molecular machines these fascinating molecular machines but once that happens this change of conformation the sodium ions are going to be released outside of the cell and then you're going to have potassium ions that are going to bind from the outside and then once that happens the change in conformation we're going to have a it's going to get D phosphorylated and then you're going to go back to your original conformation your original conformation right over here where you no longer have an affinity for potassium ions they're going to be released and then you're going to be back in the original phase so this is fascinating by using ATP by using energy this is active transport it takes energy to do this let me write this down this is active this is active transport that we are talking about right over here we're able to pump using an ATP use were able to pump three sodium ions out three sodium ions out let me write that down three sodium ions out and in the process we pump two potassium ions in so we pump two two potassium ions in now you might say okay the outside since these are both have positive charge but I have three sodium going out to potassium going in that must make the outside more positive than the inside and that actually is true but that by itself is it fully responsible it's actually only partially responsible for the for the for the electric potential difference between the inside of the membrane and the outside of the membrane what really sets that up is that you actually have channel proteins that allow potassium ions to move down to diffuse down their concentration gradients so let me let's think about what happens before I even talk about these channel proteins right over here because of the sodium potassium pump what is sodium's concentration gradient well it has a higher concentration on the outside has a higher concentration on the outside and it has a lower concentration on the inside this is sodium's concentration gradient what is potassium concentration gradient well potassium is getting pumped in from the outside into into the cell so potassium has the opposite concentration gradient it has a high concentration inside and it has a low concentration outside now if we if we let potassium go through we've talked in previous videos about ions just not being that permeate that the just the general membrane if it's not facilitated in some way isn't that permeable to things like ions like sodium and potassium ions but if you have a if you have channel proteins right over here that let the potassium get out what's going to happen well you might have one of two answers you might say well well look you know and they're things diffuse down their concentration gradient you have a higher probability since you have more potassium here than up here higher probability of them going in the right direction on this side and moving from this side to that side then you have them going from that side to that side and so you would have a net outflow of potassium and some of you might say well okay that makes sense if you only care about the concentration gradient but what happens if we look at the charge because we're saying that the inside of the cell is going to be less positive less positive and the outside of the cell is going to be more positive because it has more that we have the net ionic charges that are the same as you you want to move towards you want to move to the places that are more negative so you'd say well these potassium ions are positively charged why would they want to go from a less positive place to a more positive place and if you are saying either one of these things talk about the concentration gradient or talking about the electric potential difference you are actually going to be right in both cases these are going to be balancing forces the concentration gradient is going to allow some of these potassium ions to pour out but the concentrations the the the concentrations of potassium ions aren't going to fully equalize because of the electric potential difference because hey it's more positive out here it's less positive here when they're moving out they're going against what their charge wants to do they're going with the concentration gradient but at some point that is going to balance out and by going through this process by pumping by pumping sodium out and with that larger ratio than what you're pumping potassium in and then you further allowing more positive charge to go out you're establishing what's called the resting membrane potential for cell and this is super important for all cells but especially neuron cells or neural cells or neurons and and those are going to spend two-thirds of their energy just to establish or to keep the resting membrane potential as we'll see in the videos on neurons that's because they keep leveraging that potential to send signals down the neuron but the resting membrane potential it's less positive here and more positive there if you take if you measure this relative to let me make that a little bit neater relative to this right over here this difference this difference is depending on what estimates you look at approximately negative 70 negative 70 millivolts I've seen estimates negative 60 negative 80 negative 70 millivolts mol of millivolts and this is key for neurons what's key for all cells now the sodium potassium pump isn't just about establishing the resting membrane potential having the higher sodium concentration on the outside can also be used later on for other forms of active transport when they move down their gradient you can do things like Co transport glucose molecules so it's it these you know the biological systems are far more complicated than I often give credit for in these videos but I want to give you a full appreciation for this and just you know how big of a deal the sodium potassium pump was it was discovered in the 1950s but not in the 1997 Nobel Prize was awarded for for the discovery and of the of the sodium potassium pump and how it works
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