11. Biological Membranes and Transport
Biological Membrane Transport
Biological Membrane Transport
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Hey, guys, In this video, we're going to begin our introduction to biological membrane transport, which, of course, you guys have already covered in your old biology courses. And so this should be a piece of cake for you guys. And so recall from those old biology courses that molecules have a natural tendency to defuse down or with their concentration, Grady INTs from areas of high concentration down to areas of low concentration. And so, if we take a look at our image down below, over here on the left hand side, we'll see a little reminder of this idea from our old biology courses. And so notice Over here we have a beaker that is filled with water molecules, and this guy here is taking this dropper filled with red food coloring dye and adding one drop of red food coloring dye to our beaker. And initially in this relatively small area right here, there's quite a high concentration of red food coloring dye, whereas initially in other areas of the beaker there's quite a low concentration of the red food coloring dye. But of course, as time progresses here from left to right, because molecules had this natural tendency to defuse down their concentration. Grady INTs We know that these red food coloring dye molecules here are going to defuse from the area of high concentration two areas of low concentration like what we see here. And they will continue to do that until they reach chemical equilibrium. Which just means that the red food coloring dye molecules are evenly distributed throughout the beaker. And so that's a pretty straightforward idea from our old biology courses now also recall from our old biology courses that biological membranes are actually selectively permeable, which allows them to act as barriers to prevent or block diffusion from occurring as it naturally occurs. And so we know that selectively permissible is the same thing as semi permeable from again. Our old biology courses now permissible, is a word that's just referring to how penetrate herbal it is, how easily something can cross in and out. And of course, selectively and semi are both words that air, indicating that only some things can cross in and out. And so the term selectively permissible or semi permeable as it applies to biological membranes just means that biological membranes are incredibly picky about what they allowed to cross in and out of the cell membrane. And so if we take a look at the image down below, over here on the right hand side, we'll see a little reminder of these two ideas from our old biology courses. And so what you'll notice is right here in the middle. What we have is our biological membrane. And of course, we know biological membranes are semi permeable. And so even though there is quite a high concentration of these red molecules over here and a low concentration of the red molecules over here, and they would love to defuse right through notice that the membrane is acting as a barrier for these guys, so they're actually not able to cross and notice that the membrane to saying, Excuse me, do you read? Guys over here have an appointment to cross me. And of course, some molecules will not be able to cross. But other molecules like this yellow guy down here are able to cross of the membrane extremely easily. And so what is it that allows some member some molecules to cross the membrane easily, and other molecules have a difficult time crossing the membrane? Well, we'll talk about that in our next lesson video, so I'll see you guys there
Biological Membrane Transport
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so which molecules can freely cross a membrane without any facilitation? Well, it turns out that most of the molecules that actually can freely diffuse or freely cross a biological membrane without any facilitation whatsoever are going to be really, really small molecules that are uncharged and non polar or hydrophobic. Whereas most of the molecules that cannot freely defused without facilitation are gonna be the complete opposite. They're going to be large charged either positively or negatively charged, and they're going to be polar and or hydro Filic. And so if we take a look at our example down below, we'll be able to see the diffusion of many different types of molecules across a membrane. And so focusing over here on the left hand image first noticed that we're showing you a biological membrane right here, and we have the outside of the cell labeled as the blue background and the inside of the cell, or the site is all labeled with the yellowish background and notice that in our first category of molecules that we have over here on the left, we have 02 or Oxygen Gas Co two, or carbon dioxide gas and end to or nitrogen gas. And these are small, uncharged and non polar molecules that air hydrophobic. And these are all features that we see allow these molecules to freely diffuse across the membrane without any facilitation. And so these gasses that we see here are able to freely diffuse across the membrane. And we're representing that with a big, thick arrow to represent that they're able to easily cross this membrane. Since they have all of these features that we see here now moving on to the next category of molecules. What we have is a water molecule, a steroid hormone, specifically testosterone and a glycerol molecule, and which will notice is that these are small molecules, they are uncharged, but they do have polar groups on them. And so what this means is that they're starting to mix and match some of the features from above. So they are small and they are uncharged. But they have some polar groups. And so because they have most of the features that allow them to freely diffuse without facilitation, they are able to freely diffuse without facilitation. And so we're representing that with a green arrow. But notice that because they have some polar groups on them, a swell that they're not able to diffuse across the membrane quite a Z easily as this first group over here. And so that's why the green arrow is not as thick. The thick one over here represents. They can cross really, really easily. And this one here because it's thin, represents that they can cross, but not quite as easily as these other ones over here. And that's again because they have polar groups on them now moving on to this next category of molecules over here, what you'll notice is we have a glucose molecule, some ions and an amino acid here, specifically kleiss ing. And so these molecules are either charged or they are highly polar molecules so glucose, even though it does not have any charges on it. It has a lot of polar molecules in all of these hydroxyl groups, and all of those polar molecules is, uh, they're all in favor of the molecule, not being able to freely diffuse without facilitation. Of course, the chloride ion sodium ion and potassium ion all have charges on them, and so again, that's favoring that they cannot freely diffuse without facilitation and the amino acid glycerine with these ionized able groups here also has charges on it as well. And so amino acids, ions and glucose are all examples of molecules that cannot freely diffuse across the membrane. Now, in our last category down here, what we have are large macro molecules. And of course, being large is a feature of not being able to freely diffuse without facilitation. And so these large macro molecules could include poly peptides or large proteins, Polly Sacha rides and large new click assets. And they're simply just too large to squeeze between the fossil lipids so they can't squeeze between the possible lipids. And therefore they cannot diffuse across the membrane easily, especially without facilitation. And so over here on the right hand side, what we're showing you guys is a scale to represent the same exact ideas that we just talked about. And so if we take a look at the scale, what we'll see is it is a membrane permeability coefficient scale with units of centimeters per second and basically all I want you guys to know here is that the higher the value is on this scale, the higher the permeability is, and the lower the value is on this scale, the lower the permeability is so again, low permeability means it cannot freely diffuse, and high permeability means that it can freely diffuse without facilitation. And so what you'll notice is looking at the molecules that are on this scale. The oxygen, gas, carbon dioxide, gas and nitrogen gas that we talked about over here have a really, really high membrane permeability coefficient, which means that they can diffuse really, really easily across the membrane. Just like what we already discussed. Notice that water, testosterone and glycerol all still can freely diffuse across the membrane, but not quite as easily as these gasses glucose, even though it is small and uncharged. It's really, really polar with a lot of polar groups, so it's not able to freely diffuse across the membrane. Then you can see all of the ions. The chloride, potassium and sodium ions all have charges, so again they're not able to freely diffuse across the membrane and glazing. It's an amino acid that has thes charges as well. So again, it's not able to freely diffuse across the membrane with a really low permeability coefficient. And so really, it's just that idea here. Not that you need to memorize any of these numbers or values or anything like that. It's just this idea of showing that if you are small, uncharged and non polar hydrophobic, you'll be able to defuse pretty easily. And if you are the complete opposite large charged and polar hydro Filic, you won't be able to diffuse as easily. And really, that's the main take away of this video. And so that concludes this video, and I'll see you guys in our practice video.
Which molecule most easily diffuses across a biological membrane’s lipid bilayer, without facilitation?
Rank the unfacilitated transmembrane diffusion of the following molecules from least → most permeable.
Acetamide → Urea → Butyramide.
Urea → Acetamide → Butyramide.
Butyramide → Acetamide → Urea.
Acetamide → Butyramide → Urea.
Urea → Butyramide → Acetamide.
Biological Membrane Transport
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in this video, we're going to introduce our map of the entire lesson on biological membrane transport. And so what's important to note is that molecular transport across biological membranes can occur in a wide variety of ways, as you can see by our membrane transport map down below. And so immediately we categorize membrane transport into two different branches. The left branch over here, which is molecular transport or the transport of very small molecules. And then we have the right branch over here, which is macro molecular transport or the transport of very large molecules and small molecules as well. And so, just like the lipid map that we use in our previous lesson videos to cover lipids. This map here on biological membrane transport is a reflection of our entire lesson on biological membrane transport, and so you can use it to make predictions about what topics we're going to cover and the order of the topics that we're going to cover. So you could make a prediction as to what topic we're going to cover next. And so the way that this map works is we're always going to explore the left most branches first and Then, after we've explored the left, most branches first. Then we'll zoom out and start to explore other branches. And so the way this works is we're first going to explore the left branch over here with molecular transport of small molecules. Then we're going to explore mawr passive transport, starting with simple than moving to facilitate it, going over here, exploring this path, zooming out and exploring all of these paths. Then, once we've explored, all of those will zoom out and explored active transport again, starting with left and making our way to the right. And then finally, once we cover both passive and active transport, we'll zoom all the way back out and explore this rate branch over here with macro molecular transport again exploring left most branches first and then making our way to the right. And so this year concludes our introduction to our map of the entire lesson on biological membrane transport, and you should continuously referred to this map as we move along in our lessons. And so I'll see you guys in our next video where we'll start to explore our left branch over here. So I'll see you guys there