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  • Hi. It's Mr. Andersen and in this podcast I am going to take you on a tour

  • of the cell. We're going to talk about the different types of cells and then how the

  • structures inside a cell fit their function.

  • The first thing though that we need to talk

  • about is why cells are small. The reason cells are small is that material moves into a cell

  • through a process called diffusion. So oxygen get's in that way and carbon dioxide is going

  • to move out in the same way. And so it would take a long time for material to diffuse into

  • a cell. And so what we can do, is we can actually make that volume the same but we can increase

  • the surface area. And now the distance that material has to move is actually relatively

  • small. And you also might also think to yourself, why are the infinitely small? Why are they

  • really really tiny? Well the reason why is that the material inside a cell, the information

  • inside the cell, like the DNA and the machinery of the cell, has to be able to fit inside

  • the cell. And so there's like a perfect sweet spot in size for all the different types of

  • cells that we have.

  • Another thing I want to talk about is cells are not boring. When I grew up I had this

  • idea that a cell was like a bag of jelly and you had stuff like a nucleus inside it and

  • it would essentially float around. This is probably perpetuated by biology teachers always

  • in assigning like an edible cell assignment. And if you actually look inside a cell, it's

  • incredibly complex. They have this cytoskeleton that's made up of a number of different macromolecules.

  • It's like a lattice inside the cell. And all the organelles fit within that lattice and

  • it works almost like the monorail. As materials moved around on this monorail using these

  • motor proteins. And I'm not joking, they literally walk like that on the monorail. And so they're

  • incredibly complex, cells are. But they're often times misunderstood and they were totally

  • invisible to scientists until we invented the microscope. In other words, we couldn't

  • see them. If you look at your hand, you can't see the cells.

  • And scientists couldn't see them either so

  • they didn't know what was going on until they discovered and invented the microscope. It

  • comes in two different types. You basically have optical microscopes and then electron

  • microscopes. Optical microscopes use light and lenses to magnify the image. If you've

  • ever used binoculars and then you turn it upside down and hold it close to your hand

  • you actually have a real simple microscope. And so that's the way that they work.

  • If it's an electron microscope, what they're

  • using is a number of magnets. And those magnets will be used to focus electrons either through

  • an image or bouncing it off an image. So we've got transmission and scanning electron microscopes.

  • How does this work? Well a quick demo would be to take a big magnet and hold it really

  • close to an old television or your computer screen. Don't Do This! If you were to do it,

  • it would permanently ruin your monitor or your computer screen, but basically what it's

  • doing is the magnet is changing the path of the electrons and by doing that we can

  • actually increase the magnification of the specimen.

  • So here's some pictures that were taken with

  • these. This would be paramecium with an optical microscope, one that you have in a typical

  • biology classroom. These ones are taken by a transmission electron microscope. These

  • are little viruses. Or this would be an ant that you're looking at. Now these two are

  • dead. Because the material, in order to look at it, the process is actually going to destroy it.

  • In fact in here you have to put a thin layer of metal on it that we can bounce it

  • off on a scanning electron microscope.

  • And so the future is electron microscopes but it's also what are called fluorescent

  • optical microscopes. So we're coming up with these beautiful fluorescent dyes, and you

  • saw one on the first page in this podcast. And that we can stain material that can stay

  • alive. I even saw one stain this last summer that was a live-dead stain. And so you would

  • stain it and it would show you all the cells that were alive at that point and dead at

  • that point. It's really cool. We're getting some great visualization of the cell.

  • First thing you should know is there are two

  • major types of cells. We have what are called prokaryotic cells and then eukaryotic cells.

  • Prokaryotic cells are going to lack a nucleus. They're before the egg if we break down that word.

  • So there's going to be no nucleus. Eukaryotic cells are going to have nucleus.

  • What types of things are prokaryotic? Really

  • only two things, bacteria are going to be prokaryotic and the the archaea bacteria,

  • let me try to spell that correctly, are going to be prokaryotic. Eukaryotic are going to

  • be things you think of as alive that aren't microscopic. Things like plants, animals,

  • fungus, protists, things like that that are really really large. The scale is bad here

  • because if I were to scale it right, the bacteria would be about the size of this mitochondria.

  • So these are really, really small. But there's some similarities between the two. In other

  • words, all cells are going to have nucleic material. So they're going to have DNA.

  • All cells are going to have a cell membrane around the outside, some form of cytosol on the inside

  • and they're also going to have ribosomes. They may differ but all cells are going to

  • have those things.

  • As we move to eukaryotic cells, let me go back again, then we're going to have organelles,

  • so we're going to have organs within the cell that you're familiar with. Like a mitochondria

  • would be an example of that. And so basically prokaryotic cells are simpler, I'll talk more

  • about them when I talk about bacteria, but most of the time in this podcast I'm going

  • to talk about eukaryotic cells. This would be an animal cell, I could tell right away.

  • And so let's kinda look through an animal

  • cell. So basically these are the major organelles that are found within a cell, from the nucleus

  • all the way down to the centriole. And so what I'm going to do is go through it, show

  • you where they are, talk about what they do and then you probably want to review at the

  • end, go through all of them and see how much of the information that you have actually

  • picked up.

  • So let's start with number 1and that's the nucleolus. Nucleolus is going to be found

  • within the nucleus. And I used to be confused on how this actually works. What they do is

  • all the chromosomes that are within the nucleus, what they do is they put all of their genes

  • to make ribosomes in one area within the nucleus. And that as a result, since we have a lot

  • of proteins inside here, is going to be a little darker when it gets stained. And so

  • this is an area where the chromosomes are all producing ribosomal RNA to make the ribosomes.

  • It's going to be right there. It's kind of a two step process. So basically what happens

  • is in this area they're going to produce ribosomal RNA, it'll roll out here, it'll actually build

  • some of the proteins using ribosomes outside of the cytoplasm and then those proteins will

  • move back where we assemble the building blocks of proteins which are going to be ribosomes.

  • And so I talked about a lot of different things. But what did I mean to talk about, well the

  • nucleolus is an area where the ribosomes are assembled inside the nucleus.

  • If we go to the next one, the next one is

  • going to be the nucleus and that's one of the first organelles that was ever discovered.

  • This is a beautiful fluorescent dye on the nuclei. So what's the function of the nucleus?

  • Well, when I grew up I always heard it's like the brain of the cell. That's really oversimplifying

  • it. What's inside here? Basically we've got DNA, so the genetic material of the cell is

  • going to be found inside the nucleus and that's going to determine you know, what kind of

  • cell it's going to become. But it is also going to control the cell. In other words

  • we're going to make proteins. We're going to make enzymes at a certain time and as a

  • result of that a cells going to do something. And so if you still want to think that it's

  • the control center of the cell, that's okay. But a better way to think about it is just

  • where the genetic material is. And it's also going to have little pores on the outside

  • that will become important when we starting talking about transcription and translation.

  • So they're going to be little holes on it. And that's how material can move out and material

  • can move in through those little holes.

  • Okay. Next we get to the ribosome. Ribosome generally growing up I represented those as

  • little dots inside the cell. It's a little more complex than that. The two parts of it,

  • you're going to have a small subunit on the bottom. You're going to have a large subunit

  • on the top. And the messenger RNA is going to move through that and then on the top we're

  • going to bring in the transfer RNA and we're actually going to build our protein off of

  • it. And so the function of the ribosome is going to be to build proteins. And prokaryotic

  • and eukaryotic have different ribosomes and that's how some of our antibiotics actually work.

  • A vesicle is a broad term. A vesicle basically means a membrane bound container. And they're

  • really really small and sometimes they're really really big. So a vacuole would be an

  • example of a vesicle. And they move material around, depending on what they do. Like a

  • transport vesicle would move material around.

  • Next we get to the level of the rough ER or the rough endoplasmic reticulum. It's actually

  • a membrane that is continuous with the nucleus. And so we've got this folded membrane and

  • it comes out from the nucleus. You then have ribosomes that are sitting on the outside

  • of it. That's why it's called rough ER. I like to think of this as the factory inside

  • of a cell. And so basically what you're going to have is this membrane. So we've got a membrane

  • like this and then you're just going to have a ribosome that sits on the top of it. So

  • basically what you can do is as the messenger RNA comes through we can make the proteins

  • that we want to make. And so it's like a factory. It's going to be where we make the material.

  • It also will produce the membranes that are going to be used within the cell.

  • Next we get to the level of the Golgi Body.

  • I like to think it looks kind of like a pita bread that is folded on top of itself. So if

  • we were to say where are these proteins going? They're going to be created in the endoplasmic

  • reticulum. They'll then be packaged in a little transport vesicle and moved to the Golgi apparatus.

  • At the Golgi apparatus we're going to modify that. We're going to add things like carbohydrates

  • to those proteins. We're going to snaz them up a little bit and then we are going to send

  • them on their way. So another way to think about that is that it's like a UPS. In other

  • words it is a shipping part of the cell. Things come in as a transport vesicle. They're going

  • to go out as a transport vesicle and they're going to to where they need to go within the

  • cell.

  • Next we've got the cytoskeleton. Cytoskeleton is the structure inside the cell. It actually

  • gives it that physical structure. If a cell were to move around that's going to have to

  • be like an amoeba that's going to do with a cytoskeleton as well. The way I like to

  • think about this is through analogy. So it's kind of like a bridge. So on a bridge you're

  • going to have two things. Those are going to be supporting the bridge. But then you're

  • going to have these really thin wires that attach it up, like on the Golden Gate Bridge.

  • And so basically inside a cell we have those two things. We have the big things. Those

  • are called microtubules and they're made from a protein called tubulin. And then we have

  • these really thin things and those are called microfilaments. And what the big things, the

  • microtubules do is they provide compressional support, just like the weight of the bridge

  • is supported by them. And then those thin microfilaments are going to provide tensional

  • support. And so if you think of a cell like the Golden Gate Bridge but kind of inverted

  • inside it, that's a good way to think about what a cytoskeleton is.

  • Next we get to the smooth ER. What's it missing?

  • Ribosomes. What's it producing? It's going to produce a lot of the lipids, cholesterol,

  • things like that in the cell. It's also really really important in detoxification, so breaking

  • down toxins. And so if you're an alcoholic, hopefully not, but if you're an alcoholic

  • basically the more you drink the more your body is going to build up smooth ER inside

  • it's cell. So you're going to have to drink more and more and more and more.

  • Next we've go the mitochondria. Mitochondria

  • you know is the area where we're going to generate energy. What's it really generating?

  • That's going to be ATP, in the form of ATP. It basically has a folded membrane inside

  • a membrane. It looks a lot like a bacteria and that's because scientists think they became

  • parts of our cells through endosymbiotic theory. In other words, they became parts of the cell,

  • they produce ATP for that cell and then they get a place to live. What's some evidence

  • for that? Well, they have their own DNA they produce on their own through binary fission.

  • And so it's pretty much accepted as a biological fact.

  • Now we have the vacuole. Vacuole is going

  • to be something that we find inside plants not in animals, generally large vacuoles.

  • And in this plant cell here what it's doing is it's storing water, so it stores that balance

  • and pressure, that turgor pressure that keeps the cell properly inflated. Some protists

  • will actually have a contractile vacuole that can pump water out when they're living in

  • a fresh water environment as well. We've got vacuoles but they're really small in general

  • in animals and they're used for like endo and exocytosis.

  • Next we've got the cytosol. Cytosol, you can

  • think of as like the dissolved material so its the fluid but it actually contains solutes

  • inside it. We used to think that was about it, but what we are finding is there are concentration

  • gradients within the cell. And so even the cytosol itself is pretty complex.

  • Next we go to the level of the lysosome. The

  • lysosome is going to be, sometimes it's be coined as like the suicide sac. What does

  • it really have inside it? It has these digestive enzymes inside it and it's contained within

  • this membrane. And so basically what we can do is we could have that go next to another

  • vesicle that has material that we want to break down and those digestive enzymes will

  • go in there and it'll break it down. Or where it gets its name from is if we were to pop

  • this lysosome basically what happens is those digestive enzymes would go throughout the

  • cell and would kill the cell, dissolve the cell. And so the process of apoptosis, where

  • the cell kills itself, is a product of lysosomes.

  • And finally we have the centriole. Centriole is part of what's called the centrosome. And

  • basically its important in positioning within the cell. So dependent upon where the centriole

  • is, its also going to set up where the nucleus is going to be and where the other parts of

  • the cell are going to be. It's also important as a cell divides. It's going to be, as it

  • migrates to either side it's going to initiate the formation of the spindle. And the spindle

  • is going to be attached to the chromosomes and going to pull it to either side. And so

  • we have those but if you were looking to higher plants, they don't have centrioles and their

  • role is somewhat undefined.

  • And I think we could say the same thing for all of these. That we really have an idea

  • of what they do, but they probably do lots of other things that we're really not familiar with.

  • And so this is where the podcast becomes scary. I'm going to make all those terms disappear

  • and basically if you hit pause, could you go though at the beginning and list what is

  • number 1? What is number 2? What is number 3? What is number 4? What does number 1 do?

  • And if you can't do that, you really don't understand it. And working with kids in class,

  • what I found that when you're trying to learn the parts of the cell, sometimes it's easier

  • to just build some flash cards and go through the flash cards because if you can't get it

  • right now, then you don't got it.

  • And so that's the tour of the cell and I hope it was fun and I hope that was helpful.

Hi. It's Mr. Andersen and in this podcast I am going to take you on a tour

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セルのツアー (A Tour of the Cell)

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    wshuang999 に公開 2021 年 01 月 14 日
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