Membrane Transport of Ions - Video Tutorials & Practice Problems
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Membrane Transport of Ions
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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 leftmost 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 erythrocyte glucose uniporter GLUT 1 and the erythrocyte chloride bicarbonate antiporter. And so now we're going to explore a new branch here talking more about these points and channels, and we're gonna build up the knowledge that we need to understand the 5 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.
2
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Membrane Transport of Ions
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6m
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In this video, we're going to begin talking about membrane transport of ions. And really the main takeaway of this video is that charged ions flow down their electrochemical gradients. And we'll talk about exactly what that means here very shortly. Now the direction that charged ions diffuse across membranes actually depends on 2 different factors. Number 1, it depends on the actual charge of the ion, whether or not it is positively or negatively charged. And number 2, it depends on this electrochemical gradient as we've already mentioned. But what exactly is this electrochemical gradient? Well, the electrochemical gradient is actually based on 2 different roots, and so you can see that it has this electro prefix referring to electrical, and then it also has this chemical root as well. And so the electrochemical gradient is really just a combination and a balance of the following 2 gradients. The first gradient is the chemical gradient, and the second gradient is the electrical gradient. And so what you can see down below in our image is that if you take the chemical gradient and add the electrical gradient right here, what you'll get is the electrochemical gradient. And so let's talk a little bit more about each of these gradients to distinguish them. And so the chemical gradient here is actually the standard chemical concentration gradient that we usually refer to and so you guys are already familiar with the chemical gradient. And so just to be clear here, the chemical gradient is referring to a difference in chemical concentration between 2 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 gradients 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 gradient, 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, substance to diffuse down its chemical concentration gradient 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 gradient. But how about this electrical gradient here? How does this work? Well the electrical electrical gradient is different than the chemical gradient. The electrical gradient is not based on a difference in chemical concentration between 2 regions, It's based on a difference in the sum of electrical charges between 2 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 gradient whereas uncharged ions won't respond to the electrical gradient. And so charged ions, they will specifically flow towards the oppositely 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 0. 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 gradient. And the first thing to notice here is that we have our membrane right here, and we have 2 different regions. We have this left side which is positively charged region. It 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, only charged ions are gonna respond to the electrical gradient. And so here we have a positively charged ion and it's going to respond to this electrical gradient right here by flowing towards the oppositely 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 gradient works. And again, because the electrochemical gradient is a combination of these 2 gradients, 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 gradient on one end and we have electrical gradient on the other. And so charged ions are gonna respond to both of these gradients, whereas uncharged ions only respond to the chemical gradient. And so in some cases, the chemical gradient will overpower the electrical gradient, and in other cases, the electrical gradient will overpower the chemical gradient. And really, the electrochemical gradient is a balance of the 2. And so this here concludes our introduction to how charged ions flow down their electrochemical gradients and, we'll be able to talk more and more 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.
3
concept
Membrane Transport of Ions
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7m
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In this video, we're going to introduce the transmembrane potential. Now the transmembrane potential is also commonly referred to as the transmembrane voltage. And it can be abbreviated either as Delta Psi or as VM, depending on your textbook. Now moving forward in our clutch prep biochemistry course, we're going to use delta psi to represent the transmembrane potential. Now the transmembrane potential or transmembrane voltage is really just defined as the difference in electrical charge between the inside and the outside of a cell's 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 2 different ways to represent the transmembrane potential delta Psi. And so we've got this top way of representing the transmembrane potential and then we've got this bottom way of representing the transmembrane 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 Psi 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 cell's plasma membrane. And so if, we call this the final side of the plasma membrane, the inside of the cell, so psi in, and if we call the initial side of the membrane the outside of the cell or psi out, Then the transmembrane potential delta Psi 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 psi out, And if we call the initial side of the membrane the inside of the cell or psi in, then you can see that the transmembrane potential delta Psi 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 transmembrane potential or transmembrane voltage is that usually in your textbooks and your professors, they are going to present the transmembrane potential or voltage 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 Transmembrane Potential in your textbooks and so, that's important to keep in mind. And also usually, the transmembrane potential will be expressed in units of either volts or millivolts, v or mv. And also what's important to keep in mind here is that generally on the inside of cells, the inside of cells will be more 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 transmembrane potential is usually going to be presented as a negative value. And so, again, usually, this top equation here is gonna be used to represent the transmembrane potential. And that's why in a lot of your textbooks, you'll see that examples of resting transmembrane potential are gonna be have negative values, such as negative 70 millivolts, 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 we have a cell's plasma membrane over here. And one thing that's very important to note here is that the inside of the cell right here is more 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 of the cell is 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 transmembrane potential. And so one thing that's important to note about the transmembrane 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 a membrane, and so we're doing psi in minus psi out if it's negative. But if it's a positive value, then that means that we're looking at it from perspective of psi out minus psi in. Now when the transmembrane potential does not equal a value of 0, so if it's any other value other than 0, then what this means is that it's going to establish opposite electrical gradients for cations and anions or anions and cations. Recall anions are negatively charged and cations are positively charged. And so what you'll notice here is that because we have this transmembrane potential here, that is not equal to 0, there's a difference in the electrical charges between the inside and outside of the membrane. It's establishing an electrical gradient for anions where it's going to be attracted to its oppositely charged region. So anions like this guy right here, because of its electrical gradient are gonna want to diffuse to the oppositely charged region on the outside of the cell which is more positive. And of course, cations are gonna have the opposite electrical gradient where they're going to want to diffuse to their oppositely charged region, which would be towards the inside of the cell, which has a negative charge associated with it. And so, really, the main takeaway here in this video is that the transmembrane 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 transmembrane potential is not equal to 0 that's going to establish electrical gradients for anions and cations in opposite directions. And so this here concludes our introduction to the transmembrane potential. And as we move forward in our course, we'll be able to apply the transmembrane potential in different scenarios. And so I'll see you guys in our next video.
4
concept
Membrane Transport of Ions
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39s
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So now that we know a little bit about the membrane transport of ions in terms of charged ions diffusing down their electrochemical gradients and in terms of charged ions diffusing across a membrane with respect to the transmembrane potential. We're now going to move on and talk about the 5 types of ion channels that allow ions to passively diffuse across a membrane. And those 5 ion channels include the ion channels that are listed here on our map. And so again, we'll talk about these 5 ion channels in our next lesson video. So I'll see you guys there.
5
concept
Membrane Transport of Ions
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7m
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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 5 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 the 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 their electrochemical gradients. 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 gradient. And really the biggest takeaway here of the leakage ion channel is that they always remain open. Now moving on to the other types of ion channels, 2, 3, 4, and 5, what's important to note is that these are 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 to allow the ions to diffuse across and then also to block the ions from diffusing across. And so, what's important to note about these gated ion channels, 2, 3, 4, and 5, 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 ligand gated ion channel down below here, is on the left hand side, it is in its closed, port, version. And so this closed version does not allow the transport of ions across the membrane. However, the ligand gated, ion channel will open in response to an extracellular ligand. And so when this ligand molecule binds to the ligand 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 gradient. And so again, ligand gated ion channels respond to extracellular ligands to open up. Now the 3rd type of, 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 the 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, an intracellular signal molecule binds to it, it will open up to allow the transport of the ion across the membrane down its electrochemical gradient. And so really the biggest difference between the ligand gated and the signal gated is that the ligand gated is responding to an extracellular ligand, whereas the signal gated is responding to an intracellular signal. Now moving on to the 4th 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 transmembrane potential or the transmembrane voltage, delta psi. And so if we take a look at number 4 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 gonna be closed at a very specific transmembrane potential. Here, for example, a transmembrane potential of negative 50 millivolts. But, of course, when that transmembrane potential changes to a different value, such as, for example, negative 70 millivolts, then the voltage gated ion channel can open up so that the, ion is able to be transported across the membrane down its electrochemical 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 5 down below, the mechanical gated ion channel. Again, notice on the left hand side, it has its 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 here concludes our lesson on the 5 different types of ion channels and as we move forward in our course, we'll be able to get some practice applying these concepts. So I'll see you guys in our next video.
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Problem
Problem
Facilitated diffusion of charged ions across a biological membrane is __________________:
A
Generally irreversible.
B
Endergonic.
C
Driven directly by ATP.
D
Not specific with respect to the type of ion.
E
Driven by a difference in the electrochemical gradient.
7
Problem
Problem
Which of the following statements is false about a signal-gated ion channel receptor?
A
They are present in the cell membrane.
B
They respond to the presence of intracellular signaling molecules.
C
Differences in membrane potential can affect whether the channel receptors are open or close.
D
They are a type of gated-ion-channel that can open and close under different conditions.
8
Problem
Problem
The voltage-gated potassium channels associated with an action potential provide an example of what type of membrane transport?