Hi. In this video, we're going to be talking about actin-based non-muscle movements. So, this video is just going to focus on movements that are non-muscle, but that actin plays a huge role in. There are three I want to mention, and there's one we're really going to talk about. The first is cell crawling. This is kind of what we imagine when we imagine an entire cell moving. Right? You may have seen videos of amoebas, but essentially, the cell is just dragging itself across the surface, for some reason. Then, and this is the one we're going to talk about most, you have chemotaxis, and this is going to be a cell responding in some way, so it's got to be moving. Remember these are movements. So, it's moving in some way in response to different chemical concentrations, something that's entered its environment. So, if it gets more calcium, or more acid, or, you know, something, any kind of chemical comes into its environment, then the cell will respond by moving. It's chemotaxis. And then we have this really cool thing that I really actually like, I wish we were talking about it more, but this is cytoplasmic streaming. And so, this is where the outside of the cell is really staying stationary, but inside the cell, you can see these, like, almost like waves, these oceans of cytosol, sort of moving back and forth. They're more like streams or rivers, like fast-moving streams and rivers, to a cell, where the cytosol will actually move back and forth in the cell. And you can see that in plant cells and slime molds. So, if you ever look at a plant cell under a microscope, which you may in your labs, you can actually see this, under a microscope if you kind of know what you're looking for. But, we're not actually going to talk about that one that much; instead, we're going to focus on cell crawling. And so, cell crawling uses four steps to move across the surface. So, the first step is the protrusion step, which means that the cell has these actin-based protrusions that it extends out of its surface, and these protrusions are, you know, made up of actin, and so as they, sort of, grow and protrude out of themselves, that's going to be acting, growing, and protruding out the plasma membrane. So, what we call these protrusions differs depending on the cell type and things. So, the one you are probably most familiar with or may have heard of before is pseudopodia, that's going to be the protrusions you find in amoeba. But there are other ones, lamellipodia, and, this is going to be a leading portion of the cell and, actually, the actual protrusion is called the filopodia at the leading edge. And those are found in other organisms. But if you see any of these names in your books, know that this is what it's talking about, this protrusion step. Then, we have this protrusion, it's out there, it's stuck itself out, but then it has to attach to the surface, whatever surface it's on, whether it's on a tissue or whether it's on plastic or, you know, no matter where it's on slime, wherever it is, it's got to attach to that surface. And how it does this is it attaches through proteins called integrins, and integrins are actually on the cell, they're transmembrane proteins, they're going to be on the plasma membrane on the cell surface, and they attach, they are what attached to either the extracellular matrix or the surface where the cell is crawling. So, integrins are found on these protrusions, and that's what allows them to stick, and attach there. So, you can kind of think of integrins like Velcro, right? So, if you, you know, attach them to a surface, that Velcro is going to stick to the surface, and so, that's what the integrins do. Then, you have translocation, and so this is where the cell dragging part comes in. So, now, you have the front part of the cell, like, reaching out. It's now Velcroed itself down to its integrins, but its behind is still like way back there. So then it starts to drag the rest of its body up, and that's called translocation. And it uses those like Velcro, those integrin bindings to, like, help itself pull. Right? Because if it wasn't attached, it might just like shrink back to where it was before. But because it's attached here at these proteins, it's not going anywhere, it's going to anchor itself there, so the rest of it is just going to be dragged forward instead of the opposite thing occurring. And then, you have finally detachment, so once the butt gets up there to the front, then, those probes that Velcro or these integrins is that, okay, I've done my job, so then they release and start the process over. So these are what these protrusions look like, these are from amoebas, you can see these, they can kind of look like scary things. Essentially, they can go from really any surface and extend forward and help pull the cell along. So that is, cell crawling, I think. Yeah, that's it. So now, let's move on.
15. Cytoskeleton and Cell Movement
Actin Based Movement
15. Cytoskeleton and Cell Movement
Actin Based Movement - Video Tutorials & Practice Problems
1
concept
Cell Crawling
Video duration:
5mPlay a video:
Video transcript
2
Problem
ProblemPseudopodia are used by ameobas for cell crawling.
A
True
B
False
3
Problem
ProblemWhich of the following proteins are used so that the cell can attach to the surface on which it is crawling?
A
ECM proteins
B
Filaments
C
Filopedia
D
Integrins