- [Instructor] You might already have some type of a notion
of a what a cell is.
You might already realize that it is most basic unit
of life.
Some would argue that maybe viruses
are even a more basic unit of life,
but the organisms that we consider living, like ourselves,
are made up of cells and all living organisms
that we for sure consider living are made up of at least
one cell, so the most basic unit of life.
For example, me, this thing that's making a video right now,
I'm made up of tens of trillions of these cells.
Now a common misconception is
well these things must be small
and they indeed are very, very, very small.
Some cells are on the order of one micrometer long
and a micrometer is one-millionth of a meter,
or you could just say one-thousandth of a millimeter,
and so when you think of something that small,
sometimes there's an assumption that it must be simple,
but you could not be more wrong if you assume
that a cell is simple.
This right over here is a picture of a budding yeast cell.
You can see that it's budding off right over here,
but this just begins to show you some of the complexity
of the cell itself or of any cell,
and whereas in other videos, we're gonna talk about
different types of cells, different types of structures
you'll see in some cells versus others,
this right here is eukaryotic cell
which we will talk more about in other videos.
Now all cells have a membrane that separate it
from the outside world.
You see the membrane right over here.
This is just a cross section.
You could imagine a three-dimensional version of this.
So this is the cell, cell membrane.
It kind of defines the cell in some way,
and in general, the things inside the cell membrane
is considered the cytoplasm, cytoplasm.
Sometimes you'll hear the term cytosol.
The cytoplasm includes not just the fluid
but also all of the stuff in the fluid
while the cytosol is referring to the fluid alone
and then depending on the complexity of a cell,
so this is right here, this is a yeast cell,
this is a eukaryotic cell which we cover in more depth
in other videos but one of the features of a eukaryotic cell
is that you'll have a membrane-bound nucleus.
Now you see it in this diagram right over here.
This is not a common feature to all cells
but the only reason why I'm mentioning it in this video is
officially, the cytoplasm does not include the stuff inside
the nucleus.
In a eukaryotic cell, that is called the nucleoplasm
but we'll talk more about that in other videos.
Now another feature that is common to all cells
is the notion of a ribosome,
and this picture is full of ribosomes.
All of these little dots right here, these little red dots,
let me change my pen color,
all of these little red dots here, these are ribosomes,
and you might assume, "Wow. These are so small
"compared to this already small thing, this cell.
"Surely they are simple,"
but they're actually fairly complex RNA
and protein structures, that are, their main function is
producing protein, producing protein.
You can view these as almost the protein factories
of living organisms.
They can take genetic information in the form of RNA
and produce proteins out of them, and you can see
this cell is full of ribosomes and we're going to talk about
the different types of ribosomes in a future video.
Now another thing that is typical in most cells
is genetic information, and typically,
that genetic information is stored as DNA.
Now I say in most cells because it turns out
that even in our bodies, mature red blood cells
don't have any DNA anymore and there's other cells
that do the same thing, but in general,
in order for a cell to function and replicate,
it needs some genetic information and that is stored in DNA,
and that's true in both prokaryotic cells
and eukaryotic cells.
Prokaryotes are ones that don't have a well-defined nucleus
and membrane-bound what we call organelles,
which are these substructures in cells
which we will talk more about in other videos.
In a prokaryotic cell, the DNA is just floating around
in the cytoplasm, while in a eukaryotic cell, the DNA,
for the most part, is inside of your nucleus
and it is part of the nucleoplasm.
So I'll leave you there for now.
The last thing I want you to appreciate is just the scale.
As I mentioned, cells are small.
This picture of a yeast cell right over here,
this is a micrometer, on this scale, it would be about,
it would be about that.
That would be one micrometer, and to put that in context,
the width of a human hair,
and it actually depends on your hair, whether it's soft
or it's more like my hair and it kind of sticks up
and it's, you have thicker hair,
but if this is a human hair right over here,
this is the width of a human hair, this thing,
its width is anywhere from 20 to 180 micrometers.
My thick hair is probably closer to 180 micrometers.
So one way to think about it, you could probably take
20 or so of these yeast cells end to end
and these yeast cells, these aren't even the smallest cells
by any stretch of the imagination, and put them end to end,
20 or 30 of these across one human hair
and that's what's mind-blowing because even at that scale,
you have this complexity,
and even this picture doesn't do proper justice
to the complexity.
There's all sorts of structures inside of this
that you can't even see that help transport things
and move things around and give the structure of the cell.
So I'll leave you there.
In future videos, we'll dig a little bit more into
what eukaryotic cells are, what prokaryotic cells are.
How do cells move around?
How do they work together?