Cilia and Flagella - Video Tutorials & Practice Problems
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concept
Structure
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Hi in this video, I'm going to be talking about cilia and flag ela. So you're probably familiar with these terms from an intro class. But just to review cilia and Bella organelles and they are the organelles that are really responsible for moving the entire cell. So um let's start with Celia. So cilia are actually found in groups of multiple cilia found together and they exist on the plasma membrane and they beat back and forth in one direction. And so when they do this, this can actually move the entire cell through the fluid, but it also has the ability of moving um fluid. So for instance, the liquid and the extra cellular environment, if all these cilia are moving back and forth in one direction, then all of that liquid that's there is also going to be propelled that way. Um Exactly like if you were swimming or moving water in one direction, it's just going to move that way. The same thing with the cell and cilia. And then you have flag ela. And these are typically found in a single, I mean you think of sperm, sperm is propelled through a flag ela. And so a single flat gela gela gela is plural. And these are also found on the plasma membrane, but unlike cilia, which beat back and forth, flow gela actually spin kind of like a rope. Like if you are just to spin a rope around, it would spin like that. And this is called a wave like beating pattern. And essentially this wave like beating pattern will eventually propel the cells. So for instance, sperm or protozoa cells throughout the environment that it's in. So if you were to look at what this looks like, you have flagellum here this is gonna spin like a propeller or like a rope um sort of going around and around in circles and then you have cilia which beat back and forth. You can see it going that way in this way. And both of these are responsible for entire cell movement. And despite the fact that they sort of spin differently, their structure is really similar. So the structure is dependent on the arrangement of micro tubules. So micro tubules are arranged in what is known as a nine plus two as enemy. And so what this is is this means that there are outer double its means that there are nine double its of micro tubules so spaced equally around the outside and they actually look like this. So all of these are you know sort of to draw this three D. Which I'm not very good at it. It would look like this. And these lines would be the micro tubules and each one of these things would be a double it. So each one of these has a ton of micro tubules in it. So they're spaced around the outside and then you have a central pair which is a double it placed in the center. And so the reason it's given this funny a word um is just because this a word describes all the micro tubules in addition to all the proteins that are associated with it haven't talked about any proteins that are associated. But of course there's going to be proteins. It's not just these micro tubules existing in a vacuum. And so like I said, we talked about the microchip will double its. I'll show you a better image of that in a second. But each one of these double its is distinct. So you have this doublet and you have this doublet. So the a tool which is this one has 13. You can tell it's this one because the circle is complete. Whereas this one is the b. Because the circle is not complete And this is because in the a two double what you have is you have 13. So of course it's going to be bigger. It's going to be the complete circle. And in the B you only have 10 or 11 that fuses to the a. So it's going to be smaller because it doesn't have 13. And it's fusing to that. A Dublin. And then around the micro trouble you have you have a ball of these outer double its. And each one of them is going to be connected through a variety of structures. So there's these things called inter doublet links. These are going to connect adjacent double its together. So for instance, those two if they were next to each other and there's a particular protein called Nixon and Nixon is really important for this connection. So if we were to look at what this looks like. So here we have what looks like a flag ela. But it could be a cilia. It's hard to tell because they have this very similar structure. And so what you get is you get these outer double, it's there's 123456789 outer doublet and the one central pair. And you can see that each one of these is made up of A. Or B. A. Is going to be the complete one. So it's going to be the full circle here. A. Is here. And then if you were to look at B, what you see is B. Is going to be not the complete one. It's going to be the one that looks like it's it's attaching onto A. And of course these are all connected through different proteins. Important one is called Nexon. And you can if you follow that line you can see Nexon connecting these adjacent double, its together. So it's super important. Now, one thing that I haven't talked about is this structure down here. So I do want to briefly mention that. And so this structure is called a basal body and this is the region where the microchip bills grow. And so you can see here it's at the base of this. These micro two wheels are gonna grow up here and form those outer double, it's in central pairs, but the basal body itself, it doesn't have that structure has a different structure and that structure is, it looks like this. So you can see you have these nine triplets, you have this 123 and there's nine of these triplets that go around. And that's what makes up the basal body, which then goes on to make up the entire cilia or flag ela. And if you're to zoom in, it's going to look like that with the nine double, it's on the outside and the central pair inside. Um So that's going to be the structure of cilia and flag ela. So with that let's now move on.
2
concept
Sliding Microtubule Model
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3m
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Okay, so now we're going to talk about cilia and flew to L. A. Movement. So the model that we need to talk about when we talk about their movement is called the sliding micro tutorial model and this describes how they move. So the really important protein you need to know for movement is dynamic. So remember dining in is going to be a motor protein. What do motor proteins do? They're gonna attach on the micro tubules and kind of walk their way around. And so this walking is what allows the movement of cilia and majella. Remember silly and patella are those organized they move they go back and forth that they spin and so that movement has to be initiated by something. And so this model describes it and this protein does it. So how does this work? So the Damien binds to these bi two wheels. So the b micro tubules with the head and then it starts moving towards the minus end. And then of course using A T. P. It's a motor approaching, it uses a TP to move so it binds to the B. Two bills with the head, it binds the other two bills with its with its feet and then it starts moving towards the minus end. And when it moves it ends up sliding the other to build down and it looks like it's bending. And when it bends that is what creates that movement of the cilia or the flag. Ela. And I'll show you an example picture of that in just a second. So um in summary this model here is pretty much just movement of bending. So the sliding micro trivial model takes that dining in and it walks along and while it's walking along it ends up bending the cilia or the flag ela allowing it to move. Now there's another type of movement that we don't really talk about and that's actually like what's moving inside the flag. Ela. So the intra flag ela transport is if you have a molecule at the bottom of the flag L. A. And you need it to get to the top, then intro Flagg. Eller transport is going to get it from top to bottom or bottom to top. It's going to transport it through the flag ela like from one region to another. Um But the sliding microbial model is talking about the whole organ L. Moving. So let's look at this. So we have our dining in here and you can see it's attached to these micro tubules. There are these like kind of bars keeping everything in place. And as they begin walking along the micro tubules, they begin stepping. So here they have a little step these head groups stay in place. These um these things um these barrier proteins sort of keep the micro tubules attached together at the same region. But due to the pressure of this region being attached and moving that way and this region being attached and moving this way is going to slide it called the sliding micro trivial region for our model, for a reason, and that sliding normally would just send it past each other. But because we have these barriers here, they actually end up getting stuck and they can't slide. So the only thing that they do is they bend. So because they can't slide, they get stuck, they bend. And so that's exactly what's happening here in the sliding microbial model. And so that's actually going to cause the entire cilia, so it goes throughout the entire cilia or flag ela. And it causes it to bend and that causes it to move. So that is the sliding microbial model. So with that let's move on.
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Problem
Problem
Microtubules are arranged in which of the following arrays?
A
9 + 3
B
9 + 2
C
8 + 3
D
8 + 2
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Problem
Problem
What is the name of the structure from which cilia and flagellum grow?
