Membrane Transport of Ions

Hey, guys, we're gonna quickly revisit our map of the lesson on membrane transport just to get a better idea on what we've covered and where we're headed. And so, of course, we know that we're exploring this map by following the left most branches. So we've talked about molecular transport of small molecules, specifically passive transport, distinguishing simple from facilitated passive transport. And then we talked about carriers and transporters and specific types of carriers and transporters, including the Aretha Recite Glucose unit, Porter Glue one and the Aretha recite chloride bicarbonate, anti Porter. And so now we're going to explore a new branch here talking Maura about these porn's and channels, and we're gonna build up the knowledge that we need to understand the five types of ion channels that we have here on our map. And so now that we have a better idea on where we're headed, I'll see you guys in our next video

in this video, we're going to begin talking about membrane transport of ions. And really, the main take away of this video is that charged ions flowed down there electrochemical Grady INTs, and we'll talk about exactly what that means. You're very shortly now. The direction that charged ions diffuse across membranes actually depends on two different factors. Number one. It depends on the actual charge of the ion, whether or not it is positively or negatively charged. And number two, it depends on this electrochemical Grady int, as we've already mentioned. But what exactly is this electrochemical Grady int? Well, the electrochemical Grady in is actually based on two different routes, and so you can see that it has this electro prefix referring to electrical. And then it also has this chemical route as well. And so the electrochemical Grady int is really just a combination and a balance of the following to Grady INTs. The first radiant is the chemical Grady int and the second Grady int is the electrical Grady int. And so what you can see down below in our image is that if you take the chemical Grady int and add the electrical Grady int right here. What you'll get is the electrochemical Grady int. And so let's talk a little bit Maura, about each of these Grady INTs to distinguish them. And so the chemical Grady int here is actually the standard chemical concentration radiant that we usually refer to. And so you guys are already familiar with the chemical Grady int. And so, just to be clear here, the chemical Grady Int is referring to a different and chemical concentration between two different regions where one region would either have a higher or a lower chemical concentration than the other. And so recall that chemicals have this natural tendency to flow down their chemical concentration. Grady INTs from areas of high chemical concentration down to areas of low chemical concentration. And they will continue to do that until they reach chemical equilibrium, which would mean that the chemical concentrations in both areas are equal. And so if we take a look at this part of our image down below, it's dedicated to the chemical Grady int, and what you'll notice is we have a membrane right here that is separating these two different regions the left region from the right region and the left region has a high chemical concentration of this blue substance. And so the natural tendency is for this, uh, substance to defuse down its chemical concentration. Grady int from an area of high concentration to an area of low concentration, as indicated by this blue arrow right here. So again, really nothing new here with the chemical Grady int. But how about this electrical Grady int here? How does this work? Well, the electrical electrical Grady int is different than the chemical. Grady Int the electrical Grady int is not based on a difference in chemical concentration between two regions. It's based on a difference in the sum of electrical charges between two regions where one region would have a different charge than another region, a different net charge. And so charged ions are going to respond to the electrical Grady int. Whereas uncharged ions won't respond to the electrical Grady int and so charged ions, they will specifically flow towards the opposite, Lee charged regions and they will continue to do that until they reach electrical equilibrium instead of chemical equilibrium. And so electrical equilibrium is established when the net charge of that region is equal to zero Essentially, the charges are balanced out between these regions. And so if we take a look at our image down below right here, notice this part of our image is dedicated to the electrical greedy int. And the first thing to notice here is that we have our membrane right here and we have two different regions. We have this left side which is positively charged. Region has a net positive charge and then we have this right side of the membrane over here which has a net negative charge. And so again, Onley charged ions are going to respond to the electrical Grady in. And so here we have a positively charged ion and it's going to respond to this electrical Grady int right here by flowing towards the opposite Lee charged region. And so this positively charged ion is going to flow towards the negatively charged region over here. And of course, positively charged or charged, molecules cannot cross the membrane through simple diffusion. They have to cross the membrane through facilitated diffusion, which is why we have this membrane protein right here. And so really, that's exactly how the electrical Grady int works and again because the electrochemical Grady int is a combination of these two Grady INTs. Uh, it's really just a balance of these two different forces. So you can see that we have this balance right here. And so you can see that we have the chemical Grady in on one end and we have the electrical greedy in on the other. And so charged ions are going to respond to both of these Grady INTs, whereas uncharged ions Onley respond to the chemical Grady int. And so in some cases, the chemical Grady int will overpower the electrical Grady int and in other cases, the electrical Grady it will overpower the chemical, radiant and really the electrochemical radiant is a balance of the two. And so this here concludes our introduction to how charged ions flow down there electrochemical Grady INTs. And we'll be able to talk Maura Maura about this as we move along in our course. But for now, this concludes this video and I'll see you guys in our next one

in this video, we're going to introduce the trans membrane potential now. The trans membrane potential is also commonly referred to as the trans membrane voltage, and it could be abbreviated either as Delta Sigh or as V M. Depending on your textbook. Now moving forward in our clutch prep biochemistry course, we're going to use Delta Sigh to represent the trans membrane potential. Now the trans membrane potential, or trans membrane voltage, is really just defined as the difference in electrical charge between the inside and the outside of a cells plasma membrane. And so, if we take a look at our image down below over here on the left hand side, notice that we're showing you two different ways to represent the trans membrane potential. Delta Sigh. And so we've got this top way of representing the trans membrane potential. And then we've got this bottom way of representing the trans membrane potential. And so what's important to note is that the delta symbol here, the Greek symbol Delta really what it means is the final minus the initial. And so what you can see here is that Delta Sigh is actually going to be different, depending on what we're calling the final side of the membrane and what we're calling the initial side of the cells plasma membrane. And so if we call this the final side of the plasma membrane the inside of the cell so psy in. And if we call the initial side of the membrane the outside of the cell or sigh out, then the trans membrane potential Delta Sigh is going to have a negative value associated with it. However, if we call the final side of the membrane the outside of the cell or side out, and if we call the initial side of the membrane, the inside of the cell or side in, then you can see that the trans membrane potential Delta side will have the opposite sign associated with it, a positive sign associated with it. And so the reason for this we'll talk about here very shortly now. What's important to note about the trans membrane potential or trans membrane voltage is that usually in your textbooks and your professors, they are going to present the trans membrane potential revolt ege from the relative position of inside of a cell's membrane, calling the final side of the membrane the inside of the cell. And so usually what we'll see is that this top equation is going to be used for the trans membrane potential in your textbooks. And so that's important to keep in mind. And also, usually, uh, the trans membrane potential will be expressed in units of either volts or Millie volts V or M V. And also what's important to keep in mind here is that generally on the inside of cells, the inside of cells will beam or negative with respect to the outside of the cell, which, of course, the outside of the cell will be more positive. And so what this means is that the trans membrane potential is usually going to be presented as a negative value. And so again, usually this top equation here is going to be used to represent the trans membrane potential. And that's why, in a lot of your textbooks you'll see that examples of resting trans membrane potential are gonna be have negative values, such as negative 70 million volts, which I'm sure you guys have heard before as a resting membrane potential for neuron cells or neurons. And so over here on this right image. Notice that we have a cells plasma membrane over here. And one thing that's very important to note here is that the inside of the cell right here is mawr negative with respect to the outside of the cell. And that's why we have this big negative sign and all these negative signs here to represent that again, the inside themselves more negative. And of course, this means that the outside of the cell over here is going to be more positive with respect to the inside of the cell. And so you can see that when we change what we're calling the final side and what we're calling the initial side, that's actually going to change the overall sign of the trans membrane potential. And so one thing that's important to note about the trans membrane potential is that if it's negative, then that means that we're looking at it from the perspective, the relative position of the inside of the membrane. And so we're doing Sai in minus side out if it's negative. But if it's a positive value, then that means that we're looking at it from the perspective of sight out minus side and now, when the trans membrane potential does not equal a value of zero. So if it's any other value other than zero than what this means is that it's going to establish opposite electrical Grady INTs for cat ions and an ions or an ions and cat ions recall. An ions are negatively charged, and cat ions are positively charged. And so what you'll notice here is that because we have this trans membrane potential here that is not equal to zero, there's a difference in the electrical charges between the inside and outside of the membrane. It's establishing an electrical Grady int for an ions where it's going to be attracted to its opposite. Lee charged region. So an ions like this guy right here because of its electrical Grady in are gonna want to diffuse to the opposite. We charged region on the outside of the cell, which is more positive. And of course, cat ions are gonna have the opposite electrical Grady int where they're going to want to diffuse to their opposite, Lee charged region which would be towards the inside of the cell, which has a negative charge associated with it. And so really, the main take away here in this video is that the trans membrane potential can be expressed either as a negative value or as a positive value, depending on what we're calling the final and initial sides of the membrane. Usually we'll see it associated with a negative value. And, of course, when the trans membrane potential is not equal to zero, that's going to establish electrical Grady INTs for an ions and Catalans in opposite directions. And so this year concludes our introduction to the trans membrane potential and as we move forward in our course, will be able to apply the trans membrane potential in different scenarios, and so I'll see you guys in our next video.

So now that we know a little bit about the membrane transport of ions in terms of charged ions defusing down there electrochemical Grady INTs and in terms of charged ions defusing across a membrane with respect to the trans membrane potential, we're now going to move on and talk about the five types of ion channels that allow ions to passively diffuse across a membrane. And those five ion channels include the ion channels that air listed here on our map. And so again, we'll talk about these five ion channels in our next lesson video, so I'll see you guys there.

in this video, we're going to talk about the different types of ion channels. And so, as their name implies, ion channels will selectively and passively transport very specific ions or charged atoms such as sodium ions, potassium ions and chloride ions across a membrane. And again, they will do this in a passive manner, which means that no energy is required. And so really, there are five types of ion channels that you guys should know which we're going to describe down below. And of course, the numbers for each of these ion channels corresponds with numbers that you see down below in our image. And so the very first type of ion channel that you guys should know is the leakage ion channel. And as its name implies, the leakage ion channel remains open, which means that it's always going to allow the leakage of ions down there electrochemical Grady INTs. And so, if we take a look at this part of our image over here on the left hand side, notice that we're showing you an example of a leakage ion channel, which is this orange structure that you see here embedded in the membrane, and this ion channel is specific to potassium ions K plus here. And because the leakage ion channels are always open, they're always going to allow the potassium ion here to diffuse across the membrane down its electrochemical ingredient. And really, the biggest take away here of the Leakage ion channel is that they always remain open now moving on to the other types of ion channels 234 and five. What's important to note is that these air, all gated ion channels and the gated part is pretty much exactly what it sounds like. They have pretty much a gate that can open and close toe, allow the ions to diffuse across and then also toe block the ions from defusing across. And so what's important to note about these gated ion channels 234 and five is that the gated ion channels here will all open and close in response to various stimuli. And we'll talk about those stimuli here very shortly. And so the second type of ion channel that you guys should know is the Ligand gated Ion Channel and the Ligand gated Ion Channel is going to open and close and due to regulation by an extra cellular ligand molecule. And so what you'll notice is if we take a look at the leg and gated ion channel down below here is on the left hand side. It is in its closed, uh, port version. And so this close version does not allow the transport of ions across the membrane. However, the ligand gated uh, ion channel will open in response to an extra cellular lie again. And so when this lie again molecule binds to the lie gang gated ion channel as it is over here, it will open up the gate so that the ion is actually able to cross the membrane down its electrochemical Grady int. And so again, ligand gated ion channels respond to extra cellular Liggins to open up. Now, the third type of, uh, ion channel that you guys should know is the signal gated ion channel, which is pretty similar to the Ligand gated ion channel. Except there's one difference and that is that these will open and close due to regulation by an intracellular signaling molecule. And so what you'll notice is with e signal gated ion channel Here is that again it has its closed version over here That does not allow the transport of ions across the membrane. But of course, once a signal molecule and interest cellular signal molecule binds to it, uh, it will open up to allow the transport of the ion across the membrane down its electrochemical Grady int. And so, really, the biggest difference between the ligand gated and the signal gated is that the ligand gated is responding to an extra cellular lie, Gand, whereas the signal gated is responding to an interest cellular signal now moving on to the fourth type of ion channel that you guys should know it is the voltage gated ion channel. And so the voltage gated ion channel is going to open and close due to changes in the trans membrane potential or the trans membrane voltage delta Sigh. And so, if we take a look at number four down below the voltage gated ion channels notice that it has its closed version over here on the left hand side that will not allow the transport of ions across the membrane and that is going to be closed at a very specific trans membrane potential. Here, for example, a trans membrane potential of negative 50 million volts. But of course, when that trans membrane potential changes to a different value, such as, for example, negative 70 million volts, then the voltage gated ion channel can open up so that the ion is able to be transported across the membrane down its electrochemical Grady int. And so the fifth and final type of ion channel that you guys should know is the mechanical gated ion channel, and the mechanical gated ion channel is going to open and close due to a mechanical stimulation such as, for example, touch sound or pressure. And so, if we take a look at ion Channel number five down below the mechanical gated ion channel again notice on the left hand side, it has it's closed version that will not allow the transport of ions across the membrane. But of course, the mechanical gated ion channel will respond to a mechanical stimulation such as, for example, sound and so sound could cause this mechanical gated ion channel to open up so that the transport of ions is possible across the membrane. And so really, this year concludes our lesson on the five different types of ion channels and as we move forward in our course will be able to get some practice applying these concepts, so I'll see you guys in our next video.