Actin Based Movement - Online Tutor, Practice Problems & Exam Prep

Cell crawling is a vital actin-based movement involving four key steps: protrusion, attachment, translocation, and detachment. During protrusion, actin filaments extend from the cell membrane, forming structures like pseudopodia. Attachment occurs via integrins, which anchor the cell to surfaces, akin to Velcro. Translocation involves the cell dragging its body forward, leveraging these attachments. Finally, detachment releases the integrins, allowing the process to repeat. This mechanism is crucial for processes like chemotaxis, where cells move in response to chemical gradients, showcasing the dynamic nature of cellular motility.

Cell Crawling

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.

Pseudopodia are used by ameobas for cell crawling.

• A. True
• B. False

Which 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

Here’s what students ask on this topic:

What are the four steps involved in cell crawling?

Cell crawling involves four key steps: protrusion, attachment, translocation, and detachment. During protrusion, actin filaments extend from the cell membrane, forming structures like pseudopodia. Attachment occurs via integrins, which are transmembrane proteins that anchor the cell to surfaces, similar to Velcro. Translocation is the process where the cell drags its body forward, leveraging these attachments. Finally, detachment releases the integrins, allowing the process to repeat. This mechanism is crucial for processes like chemotaxis, where cells move in response to chemical gradients, showcasing the dynamic nature of cellular motility.

How do integrins function in cell crawling?

Integrins are transmembrane proteins that play a crucial role in cell crawling by facilitating attachment. They anchor the cell to surfaces, acting like Velcro. During the attachment phase, integrins bind to the extracellular matrix or other surfaces, providing a stable point for the cell to pull itself forward during translocation. Once the cell has moved, the integrins release their hold, allowing the cell to detach and repeat the process. This attachment and detachment cycle is essential for effective cell movement.

What is chemotaxis and how is it related to actin-based movement?

Chemotaxis is the movement of a cell in response to chemical gradients in its environment. It is closely related to actin-based movement because the cell uses actin filaments to extend protrusions in the direction of higher chemical concentration. These protrusions, such as pseudopodia, are stabilized by integrins that attach to the surface, allowing the cell to pull itself forward. This dynamic process enables the cell to navigate towards favorable conditions or away from harmful stimuli, demonstrating the importance of actin in cellular motility.

What are pseudopodia and how do they function in cell movement?

Pseudopodia are actin-based protrusions that extend from the cell membrane, playing a crucial role in cell movement. During the protrusion step of cell crawling, actin filaments polymerize to push the membrane outward, forming pseudopodia. These structures then attach to the surface via integrins, providing a stable anchor. The cell can then pull its body forward during translocation, using the pseudopodia as leverage. Once the cell has moved, the pseudopodia detach, allowing the process to repeat. Pseudopodia are essential for processes like chemotaxis and amoeboid movement.

What is cytoplasmic streaming and where can it be observed?

Cytoplasmic streaming is a process where the cytosol (the liquid component inside the cell) moves in a directed flow within the cell. Unlike cell crawling, the cell's exterior remains stationary while the cytosol circulates, resembling streams or rivers. This movement helps distribute nutrients, organelles, and other materials within the cell. Cytoplasmic streaming can be observed in plant cells and slime molds. Under a microscope, you can see the cytosol moving back and forth, facilitating efficient intracellular transport and contributing to cellular function.