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.