Hi. It's Mr. Andersen and welcome to Biology Essentials video number 17. This
is on compartmentalization. What does that mean? It's a big word. What does that mean?
Well, a better way to start is to talk about why cells are small. And then another question
I can ask is why are cells not infinitely small? So why are cells small? Well first
of all let's look at the size of some of these cells. So these are eukaryotic cells. So eukaryotic
cells are mostly a little bit under a millimeter in length. Prokaryotic cells, so things like
bacteria and archaea are going to be on the order of about a micrometer. And then small
things like atoms are going to be on the level of nanometer. But it looks like life which
is going to be eukaryotes and prokaryotes are going to be right in this kind of a sweet
spot. Viruses, are they alive? Well we could argue about that for a long time. In other
words life kind of is in this area. So it has cell sizes about that big. Now why are
cells small, but not too small? If we think about it, let's look at a cell here. So if
this is a cell right here, so this the the cell membrane that goes around the outside. It's
got a certain amount of volume on the inside. And then it has surface area that goes around
the outside. So this would be the surface area that goes around the outside. So we could
figure that out. But if I were to cut that cell into four parts, what would happen to
the volume? The volume would stay the same but the surface area would increase because
we'd have all this surface area on the inside. Why is surface area good? It's because it
allows you to get more nutrients in. To have more chemical reactions going on on that membrane.
And so if I even make it smaller, we get even more surface area. And so why are cells small?
The reason cells are small is to increase the amount of surface area that you have.
A great example of that would be a piece of wood. If you try to light a big piece of wood,
you can't get it to start. But if you chop that into smaller bits of kindling or even
better yet make it into sawdust, then you can get a huge amount of flames really really
quickly because you're increasing the surface area. Or you're increasing the area along
which we can have all these complex chemical reactions. And so the goal of life is to increase
surface area. And that's going to push cells towards the small end. Now why are they not
infinitely small? Well we don't have living things this small and the reason why is that
you wouldn't be able to put hereditary material, you wouldn't be able to put the machinery
of the cell inside it. And so they can't be infinitely small. But even within this slice
of life we find that there are actually two strategies. There is the eukaryotic strategy
and the prokaryotic strategy. Prokaryotes are going to be way smaller then eukaryotes.
And how are they able to, eukaryotes, be able to be bigger? Well that's through a process
of compartmentalization. In other words instead of making themselves really really small,
they have parts inside them that are small. And that allows them specialization. And it
also allows them to increase surface area. Okay, so in this podcast I'm going to talk
about mostly eukaryotic cells. But know that cells can be prokaryotic or eukaryotic. Two
types of prokaryotic cells are bacteria and archaea. It doesn't mean that they're closely
related. We're actually more related as eukaryotes to archaea then either of us are to bacteria.
It just means that they have a similar life style. Or a similar life strategy. So the
domain eukarya shows compartmentalization. What that does is it's parts within the parts.
So it allows us to specialize. So we can have parts of a cell that do specific jobs. And
then we can increase the surface area. So we can increase the surface area of the cell
without making the cell smaller. We just have parts inside it that are smaller. Example
of one thing that does both of these is the endoplasmic reticulum. It allows specialization.
So there are a number of jobs done by the E.R. and it also increases the surface area
for that cell, for all of these chemical reactions. So archaea and bacteria, if you look at, this
is an e. coli. One of the most famous bacteria. And if you look at halobacteria which is a
salt loving archaea, they both look almost identical. And the reason they look identical
is they have a similar life style. But the one thing that ties them together is that
they're incredibly small. So this would be about 2 nanometers or 2 micrometers. And these
are about 5 micrometers. So about the same size. They have the same kind of a shape but
they're both really small. Prokaryotes are all small. That's to increase surface area.
Now inside us, we have what are called mitochondria. Mitochondria are not living on their own.
They require us for life. But they're about the same size as both archaea and bacteria.
And the reason why we think is that mitochondria used to be bacteria cells on their own that
became part of our cells. And we now use them for compartmentalization. The mitochondria
inside our cells actually make ATP. And they're folded to increase surface area. And so compartmentalization
is simply having parts within the parts. Or smaller parts inside the larger relative cell.
And so what it does is it increases surface area and increase specialization. Now our
cells aren't made of Kleenex, but Kleenex is a great example of something that shows
compartmentalization. In other words a Kleenex box has Kleenex folded inside it to increase
the surface area. In other words if you just wiped your nose on the outside of the box,
you wouldn't have much surface area to do that. And also there's going to be specialization.
In other words the box on the outside, it's job is to contain the Kleenex and the job
of the Kleenex is to wipe your nose on the inside. And so that's a real simple example
of what a cell is doing. And so just to point to a few things, these are mitochondria inside
a eukaryotic cell. Those generate ATP. This could be a lysosome inside the cell. It digests
material in the cell. This could be the golgi apparatus inside the cell. It moves material.
And this is the nucleus. It contains the DNA, contains the genetic material. And so all
these different parts of a cell have specific jobs. They do specific things. But if you
look at it, they're highly folded. And the reason they're highly folded is to increase
the surface area. The one that I want to talk about more specifically is called endoplasmic
reticulum. Endoplasmic reticulum has two different parts to it. This right here would be the rough
endoplasmic reticulum. And the reason why is if you look at it under the microscope
you see these little dots on the surface of it. And then this would be smooth endoplasmic
reticulum. But essentially endoplasmic reticulum is a folded membrane. So it's folded over
and over and over again so you have this space on the inside. But what that allows it to
do is increase the surface area but it also allows it to specialize. And so what does
the rough endoplasmic reticulum do? Well you have to start with what ribosomes do? So
here's a ribosome attached to the rough E.R. Essentially what will happen is we will have
the ribosome out here in the cytoplasm of the cell. It will start having messenger RNA
feed through it and it'll start making a protein. After it gets a little bit down on that, the
ribosome will attach to the rough E.R. and then it will actually make the protein inside
the E.R. So eventually that polypeptide will fold and it'll make a protein. And so that's
going to be what these little green dots could represent. It's going to make a protein on
the inside. And so what does rough E.R. do? Well, it really just does one thing. It makes
proteins. We can then package those proteins within vesicles. They can move their way over
to a golgi apparatus and then move somewhere else inside the cell or even outside the cell.
So rough E.R. essentially make proteins. The smooth E.R. doesn't have ribosomes on its
surface but it doesn't mean it's any less important. It's going to make lipids. It's
going to make steroids. It's going to be responsible for metabolism of carbohydrates, or breakdown
of carbohydrates. It regulates the calcium ion concentration inside the cell. It detoxifies.
It breaks down toxins inside the cell. And so the smooth E.R. shows a high amount of
specialization. It does a number of different jobs. And those aren't done by different,
other parts of the cell. It's simply done by this one part of the cell. And so that's
called an organelle. An organelle is going to essentially be a tiny organ. It's a part
of the cell that allows for specialization. An interesting side note on S.E.R. is that
alcoholics have a much higher amount of S.E.R. in their cells, especially in the liver
than a normal person cells. And that's because they're constantly breaking down alcohol and
getting rid of the toxin. And so endoplasmic reticulum is just one organelle inside eukaryotic
cells. But again what it does is increase the surface area and then does a specific
job. And so I hope that's helpful.