6. The Membrane
Introduction to Membrane Transport
Introduction to Membrane Transport
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in this video, we're going to begin our introduction to membrane transport, and so biological membranes are semi permeable. And what this means is that they can act as barriers to essentially prevent diffusion of molecules now semi permeable or, in other words, selectively permeable. Our terms that are synonyms, toe one another selectively permissible and semi permeable are synonyms and really what this means selectively, permeable or semi permeable. It just means that biological membranes they're really, really picky about what they allowed to cross the membrane and so permeable is really a word that just refers to how penetrate herbal something is and selectively just means that it's picky. It's going to select what is allowed to cross and what isn't allowed to cross on semi is basically a word that means partial and so semi permeable means partially penetrate herbal again, just meaning that it's really, really picky about what it allows to cross the membrane. So let's take a look at our example image down below at the selectively permeable biological membranes. So notice here in the middle what we have is our biological membrane, which is a semi permeable biological membrane, and notice that some molecules like this yellow molecule here are able to get through the membrane really, really easily. But not all molecules can get through the membrane. Some molecules are not able to cross, and so notice these molecules air like stupid barrier. They cannot get through, and the membrane is again acting as a barrier asked saying. Excuse me, do you read? Guys over here have an appointment to get across the membrane. And so essentially, this whole cartoon right here is just supposed to represent that membranes act as biological barriers to prevent the diffusion of some molecules. And so these red molecules are not able to diffuse across from an area of high concentration to an area of low concentration. But other molecules like this yellow one over here who's laughing at the red ones that can't get through, uh, they can get through the membrane. And so that's, um, something important to keep in mind. And so, in terms of what molecules are allowed to cross the membrane and what molecules are not allowed to cross the membrane, we'll get to talk about that in our next lesson video. So I'll see you all there
Which Molecules Freely Cross Membranes?
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So from our last lesson video, we know that biological membranes are selectively permeable or semi permeable, meaning that they act as barriers to prevent the diffusion of some molecules. But which molecules freely cross membranes and which molecules do not freely cross membranes? Well, that's exactly what we're gonna talk about in this video. Now some molecules can freely diffuse across a membrane without any facilitation from proteins whatsoever. And so the molecules that can freely diffuse across the membrane without any facilitation from a protein whatsoever are molecules that are really, really small in size molecules that air uncharged or have a neutral charge, and molecules that are non polar or hydro phobic, whereas molecules that cannot freely cross or freely diffuse across a membrane without facilitation from a protein are molecules that are really, really large molecules that are charged with either a positive or a negative charge, and molecules that air polar or hydro filic. And so, once again, molecules with these features right here cannot freely diffuse across the membrane without facilitation from a protein. But molecules that have these features at the top, they can freely diffuse across a membrane without facilitation. So let's take a look at this image down below to get a better understanding of this idea of the diffusion of molecules across the membrane. So notice over here in the top left what we're showing. You are small, uncharged, non polar molecules and so notice that they have all three of the features. They're small, they're uncharged, and they're non polar or hydrophobic molecules. And so when the molecules have all of the features, these molecules are able to cross the membrane freely without any facilitation whatsoever. And that's why we have a big, thick green arrow here to show that these molecules have no problems getting across the membrane. And so this includes molecules such as gas is like oxygen, gas and carbon dioxide gas, as well as nitrogen as well nitrogen gas. All of these molecules are capable of diffusing across the membrane with no problem whatsoever. Now notice. Over here we have some molecules that have a little bit of some mixed features here. They're small and uncharged, but notice that they are polar or at least they have some polar components. And polar is a component of features that cannot freely diffuse across. And so because these molecules have a little bit of polar notice that they can still get across the membrane. But they don't get across the membrane as easily as thes other molecules over here. And that's why we have a thin, skinny green arrow to show that they still get across, but not as easily as the ones that have all of the features that can freely diffuse. And so this includes molecules like water, and, uh, this molecule here, which is a type of steroid, and this molecule over here, which is a molecule called glycerol. And so these molecules are small and uncharged, but yet they are polar, and so they could get through the membrane, but not as easily as these other ones over here. Now, notice. Over here in this box, we're showing you molecules that are charged or polar, and so those are features alright here, charged or polar of molecules that cannot freely diffuse across the membrane. So notice that these molecules they cannot diffuse across the membrane they cannot get through the membrane without any facilitation, and notice that this last category molecules down below are large macro molecules. Macro is a prefix. That means large. So these air really, really large molecules like large poly peptides or large proteins. And a swell is large polly sack rides and nucleic acids. These molecules, because they're large, they are features of molecules that cannot freely diffuse across the membrane. So once again notice that these molecules are not able to diffuse across the membrane and so they cannot get through. And so really, this year concludes our introduction to which molecules can freely across the membranes and which molecules cannot freely across the membrane. And once again, this little table here summarizes it. What you should know. The molecules that can freely diffuse are going to be very, very small, uncharged and non polar and hydrophobic, which, whereas the molecules that cannot freely diffuse across the membrane, will be large charged, either positive or negatively charged or polar or hydro Philip. So we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you guys in our next video
Which molecule most easily diffuses across a biological membrane’s lipid bilayer, without help of a protein?
Map of the Lesson on Membrane Transport
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in this video, we're going to introduce our map of the lesson on membrane transport, which is down below right here. And so notice. At the very top of this map, we have the words membrane transport and membrane transport can really be grouped into two large categories, which is why we have two branches coming off of membrane transport, 14 molecular transport and one for bulk transport. And so molecular transport is going to be for the transportation of very, very small molecules, whereas bulk transport is going to be the transport of very, very large molecules. Now, because this, uh, image here is a map of the lesson, that means that we can use this image like a map to make predictions about what topics we're going to cover next. So we're going to be exploring this map by following the left most branches first. So we're going to start off our lesson by talking about molecular transport, uh, focusing in on passive transport, then talking about osmosis, simple diffusion and facilitated diffusion, including carriers and transporters and porn's and channels. And then, once we've explored, left most branches to there to the end, then we'll zoom back out and focus more in on the other branches. So we'll talk about active transport, distinguishing primary from secondary active transport. And then, of course, once we've explored these left most branches, then we'll zoom back out and start to explore bulk transport or the transport. A very large molecules, which includes Endo site Asus like fa go psychosis, sell eating pinot psychosis, sell drinking and receptor mediated endo psychosis. And then, of course, once we've explored, these will end the lesson by talking about, uh, XO site Asus. And so this is the way that the map can be utilized and so moving forward throughout our course. You should be referring back to this map so that you can make predictions about what topics we're covering next and also where we are within the map. And so this year concludes our introduction to the map of a lesson on membrane transport, and we'll be able to get started our with our lesson by talking about molecular transport, essentially talking about passive transport and distinguishing it from active. So I'll see you guys in our next video
According to the map above, what kind of large molecule transport is also called the process of cell “eating”?
Additional resources for Introduction to Membrane Transport
PRACTICE PROBLEMS AND ACTIVITIES (5)
- Fill in the following concept map to review the processes by which molecules move across membranes.
- Add labels to the figure that follows, which illustrates some molecules that can and cannot pass through cell ...
- Which of the following processes includes all the others? a. osmosis b. diffusion of a solute across a membran...
- How do the components and structure of cell membranes relate to the functions of membranes?
- The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered whi...