– (Voiceover) When we first learn about cells, because of the visualizations that we often see in textbooks or even some of the micrographs we might see from microscopes, we kind of imagine cells as these little balloons of fluid with things floating around in them. So, this right over here, this is a fairly common textbook visualization of a cross section of the cell and we see all of these important parts. We see the nucleus. We see the endoplasmic reticulum. We see the Golgi apparatus. We see mitochondria here. And the way that this is drawn, it looks like they’re just floating. It looks like they’re just floating in the cytosol. And it is true that there is a lot of water in cells. In fact, you are mostly water and most of that water that makes up you is found in cells. But it turns out that these types of drawings are missing a very crucial aspect of the structure of cells. They are missing the cytoskeleton. Cyto, cytoskeleton. And this is still something that we are trying to understand better of what, how does the cytoskeleton work and how does it help the cell have its structure and move things around and give it its shape. So cytoskeleton-it’s one word, but I’ve written the different parts of the words, the different parts of the word, in different colors here because this literally means “cell skeleton”. So if I were to actually try to visualize this cytoskeleton here, I have all sorts of these structures. I’ll use a different color. I have all sorts of these structures criss-crossing the cell in different ways that have proteins bound to them and they’re even moving and they’re growing and they can help the cell move around or they can help transport things within the cell and other things could be lodged in them. And so it’s a much, much, much, much more complex thing that we’re talking about than what was depicted in this visualization before I had my chance to scribble on it. And to help us visualize it, I’ve found this picture. It’s a public domain picture. And I found it fascinating cause it really helps you think about the complexity that is going on in even one of your cells. So, let’s look at some of the structures over here. So, this thing that I’m kind of tracing right over here, this is called a microfilament. This is a microfilament. Let me write that. That’s a microfilament. And just to get a sense of the scale, its diameter, so this diameter is gonna be about six or seven nanometers. So, approximately six to seven nanometers, six to seven billionths of a meter. And to have, to just get a sense of that relative to the cell itself, a typical cell could be six to seven micrometers in diameter or larger. So this is essentially one thousandth of the diameter of the cell. So these things that I am drawing right over here, these actually would not be that far off in terms of scale. In fact, I’d probably want to draw it even thinner. And that’s why you often won’t see it in these diagrams cause you would have to draw it so thin. The diameter of one of these filaments is roughly, order of magnitude, a thousandth of the diameter of a fairly typical cell. But these things are incredibly important. They help give the structure of the cell. They’re made up of actin proteins. So you can see, there’s kind of these two actin, you could kind of visualize them as ropes, wrapped around each other. And so this, the protein involved here. Let me do this. I’m using that color too much. The protein involved in these microfilaments is actin. This is actin. And what’s neat about these microfilaments in a cell, as I said, they help give structure. They help do all sorts of things. They can actually be dynamically kind of destroyed and created. Their lengths can be changed. This can help a cell actually move and even more, you can use them. You can transport things along them. You can pull and tug on them. And there’s actually a fascinating interaction between actin and what you see over here. This right over here, this is made up of myosin. This is myosin. My-let me write this. It’s hard to see. That is myosin. Myosin. And the relationship with actin, myosin can act as kind of this thing that kicks along the myosin. And they can move relative to each other. And this is essential for muscles contracting. It’s fascinating to see that even things like proteins, which are just made up of a bunch of amino acids, they can interact in these fairly complex ways that you can have these myosin things kick along and move and tug on the actin. So that’s myosin right over there. We see ribosomes. These ribosomes are the ribosomes that are not attached to the endoplasmic reticulum. So these are free ribosomes around here. So you can see it’s incredibly, incredibly complex. You might say ok, I see these microfilaments made up of actin. I see one, the one I outlined. There’s others over here. I see another one right over here. I see one up over here. But what are these big tube-like structures that we also see? So for example, what is this, what are these tube-like structures? Well these are called microtubules. So, micro, microtubules. And they look massive compared to the microfilaments, but they’re still fairly small on the cellular scale. This is about 25 nanometers. And once again these play a huge role in the structure of cells. And they allow things to be organized and things to be transported. And these are also dynamic pieces of the cell. And they can be constructed and they can be destroyed. And they can change the shape of the actual cells. And in animal cells, the things I’ve just described are found in most cells, but in animal cells, you will also find things called intermediate filaments that are actually in between these two in size which also help maintain shape and do other things. So the whole point of this video is to just give you even more appreciation. Hopefully all the other videos we’ve had on cells have given you appreciation for how much beauty and how much complexity there are in things that a lot of times on an everyday level, we think of as something as simple as a cell. But there’s all this beauty and complexity to its structure that’s often not even depicted in the drawings of the cells that you might find in your textbooks. And to get a better appreciation, here are some public domain images I found of cells where you can see the cytoskeleton actually colored in. And what you see in this picture in particular, in this yellowish-green color, this is actually cow lung cells right over here, this yellowish-green structure, these yellowish-green lines you see, those are the microtubules. And what you see in this pinkish or orangish color, these are the microfilaments. So you get a appreciation for how complex and structured these things that you used to think were just big blobs actually are.