A Tour of the Cell


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.

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