Endoplasmic reticulum and Golgi bodies

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We've already talked
about the process

from going from DNA
to messenger RNA.

And we call that
process transcription.

And this occurs in the nucleus.

And then that messenger
RNA makes its way outside

of the nucleus, and it
attaches to a ribosome.

And then it is translated
into a protein.

And so you could say that
this part right over here,

this is being facilitated
by a ribosome.

Or it's happening at a ribosome.

With that high-level
overview, I now

want to think a little bit
in more detail about how this

actually happens, or the
structure of things where

this happens inside of a cell.

And so I'm going to now draw
the nucleus in a little bit more

detail so that we
can really see what's

happening on its membrane.

So this right over
here is the nucleus.

Actually, let me
draw it like this.

And instead of just drawing the
nucleus with one single line,

I'm going to draw
it with two lines.

Because it's actually a
double bilipid membrane.

So this is one bilipid
layer right over here.

And then this is another
one right over here.

And I'm obviously not
drawing it to scale.

I'm drawing it so you can
get a sense of things.

So each of these lines
that I'm drawing,

if I were to zoom in on this--
so if I were to zoom in on each

of these lines,
so let's zoom in.

And if I got a box like that,
you would see a bilipid layer.

So a bilipid layer
looks like this.

You have the circle
is a hydrophilic end

and those lines are the
fatty hydrophobic ends.

So that's our bilipid layer.

So that's each of these lines
that I have drawn, each of them

are a bilipid layer.

So the question is, well,
how does the mRNA-- obviously

you have all this
transcription going on.

You have the DNA,
you have the mRNA.

It's all in here,
this big jumble

of chromatin inside the nucleus.

How does it make its way outside
of this double bilipid layer?

And the way it makes its way
out is through nuclear pores.

So a nuclear pore is
essentially a tunnel.

And there are
thousands of these.

It's a tunnel through
this bilipid layer.

So the tunnel is made up
of a bunch of proteins.

So this right over
here-- and this

is kind of a cross
section of it.

But you could almost
imagine it if you're

thinking of it in
three dimensions,

you would imagine a tunnel.

A protein-constructed--
a tunnel made out

of proteins that goes through
this double bilipid membrane.

And so the mRNA can make its way
out and get to a free ribosome,

and then be translated
into a protein.

But this right over here is
not the complete picture.

Because when you translate a
protein using a free ribosome,

this is for proteins that
are used inside the cell.

So let me draw the entire
cell right over here.

This is the cell.

This right over here is
the cytosol of the cell.

And you might be
sometimes confused

with the term cytosol
and cytoplasm.

Cytosol is all the fluid
between the organelles.

Cytoplasm is everything
that's inside the cell.

So it's the cytosol
and the organelles

and the stuff inside the
organelles is the cytoplasm.

So cytoplasm is everything
inside of the cell.

Cytosol is just the fluid
that's between the organelles.

So anyway, the free ribosome
over here, this translation

is good for proteins used
within the cell itself.

The proteins can then
float around the cytosol

and used in whichever
way is appropriate.

But how do you get protein
outside of the cell,

or even inside the
cellular membrane?

Not within it, within
the cell, but embedded

in the cell membrane or
outside of the cell itself.

And we know that
cells communicate

in all sorts of different
ways and they produce proteins

for other cells or for
use in the bloodstream,

or whatever it might be.

And that's what we're going
to focus on in this video.

So contiguous with this
what's called a perinuclear

space right over here, so
the space between these two

membranes-- So you have
this perinuclear space

between the inner and
outer nuclear membrane.

Let me just label that.

That's the inner
nuclear membrane.

That's the outer
nuclear membrane.

You could continue this
outer nuclear membrane,

and you get into these kind
of flaps and folds and bulges.

And this right over
here is considered

a separate organelle.

So you get this thing
that looks like this,

and I'll just do it the
best that I can draw it.

And this right
over here is called

the endoplasmic reticulum.

So this right here is
endoplasmic reticulum,

which I've always thought would
be a good name for a band.

And the endoplasmic
reticulum is key for starting

to produce and then later
on package proteins that

are either embedded in
the cellular membrane

or used outside of
the cell itself.

So how does that happen?

Well, the endoplasmic reticulum
really has two regions.

It has the rough
endoplasmic reticulum.

And the rough
endoplasmic reticulum

has a bunch of ribosomes.

So that's a free
ribosome right over here.

This is an attached ribosome.

These are ribosomes
that are attached

to the membrane of the
endoplasmic reticulum.

So this region where
you have attached

ribosomes right
over here, that is

the rough endoplasmic reticulum.

I'll call it the
rough ER for short.

Perhaps an even better
name for a band.

And then there's
another region, which

is the smooth
endoplasmic reticulum.

And the role that this
plays in protein synthesis,

or at least getting proteins
ready for the outside

of the cell, is you can
have messenger RNA-- let

me do that in that
lighter green color--

you can have
messenger RNA find one

of these ribosomes associated
with the rough endoplasmic

reticulum.

And as the protein
is translated,

it won't be translated
inside the cytosol.

It'll be translated
on the other side

of the rough
endoplasmic reticulum.

Or you could say on
the inside of it,

in the lumen of the rough
endoplasmic reticulum.

Let me make that
a little bit-- let

me draw that a
little bit better.

So let's say that this right
over here, that right over here

is the membrane of the
endoplasmic reticulum.

And then as a
protein, or as a mRNA

is being translated
into protein,

the ribosome can attach.

And let's say that
this right over here

is the mRNA that is
being translated.

Let's say it's going in that
direction right over here.

Here is the membrane of the ER.

So ER membrane.

This right over here-- and
actually, the way I've drawn it

right over here, this is
just one bilipid layer.

So let me just
draw it like this.

I could do it like this.

And this is actually, this
bilipid layer is continuous.

It's continuous with the
outer nuclear membrane.

So let me just make it like
that so you get the picture.

And then at some point in
the translation process,

the protein can be
spit out on the inside.

As it's being translated,
it can be spit out

on the inside of the
endoplasmic reticulum.

So this is the lumen.

This is the ER lumen
right over here.

So we're inside the
endoplasmic reticulum here.

Here we're outside
in the cytosol.

So that way you get the
protein now, inside the ER.

Inside the
endoplasmic reticulum,

and it can travel through it.

And at some point,
it can bud off.

So let's say, imagine the
protein is right over here.

And the smooth endoplasmic
reticulum has many functions,

and I won't get into all the
depth of how it's involved.

But at some point that
protein can bud off.

So let me draw a
budding off protein.

So let's say this
is the membrane

of the endoplasmic reticulum.

And a protein, let's say,
ends up right over here.

And then it can bud out.

So it could go from that to--
let me do that same color.

It could go from
that to that-- I

think you see where this is
going-- to that, and then

to that.

And then it could go
to something like this.

Now it has budded out.

And when you have a
protein, or really you

have anything that's
being transported

around a cell with its
own little mini membrane,

we call this a vesicle.

So now it'll bundle up,
and now it is a vesicle.

Now, this vesicle
can then-- let me

draw some of these vesicles
holding some proteins, so

let me draw that-- can then go
to the Golgi apparatus, which

I'll drawn in blue right
over here as best as I can.

So the Golgi apparatus.

This is not--
obviously there could

be better drawings of
something like this.

And then they can essentially
do the reverse process,

and they can attach themselves
to the Golgi, oftentimes

the Golgi body, named after
Mr. Golgi who discovered this.

And then the proteins,
once they get

into the inside
of the Golgi body,

then they essentially go
into a maturation process

so that they're ready for
transport outside of the cell,

or maybe to be embedded
into the cellular membrane.

So this right over
here is the Golgi body,

or a Golgi body or
Golgi apparatus.

And then once they're
done with that process,

then this is kind of the
fully-manufactured protein

ready to be used.

And actually, maybe I'll make
it a slightly different-- well,

I'll just use that same color.

This is the
fully-manufactured protein.

And now it can transport
to the cell membrane.

And that protein can
either be transported

outside of the
cell, or it can be

embedded within the
membrane itself.