We said that microtubules form highway through the cells.
So how would I get something made in the cell body of this neuron
all the way to the other end of the neuron?
Along these highways. But you cannot just crawl along the highway.
It turns out that we're learning that there are some
really fantastic machinery going on inside the cells too.
There are actual molecular motors.
Now if you had to make a molecular motor that was going to
move along one of these microtubule highways,
what sorts of things do you think you would need?
You'd first need probably something to carry the stuff,
and a place for it to sit, and a way to attach it
and then some means of propulsion, right.
And so that's exactly what the cell has done to overcome this need
to transport things down the microtubules.
So here we go.
We could have an actual organelle that's being moved.
Maybe we're moving mitochondria to the other end of the cell
because we need to get some energy going down there.
Or maybe we're moving a load of neurotransmitter
that's just been made up in the cell body and
we need to move that down to the end of the neuron.
So we stick it on this little vehicle,
which is our cellular motor.
And we give it a platform and a means of propulsion.
So dynactin are these proteins that allow movement
or motor proteins that allow movement
pushing the vehicle along that microtubule.
Now we need the motor to be stablized on there
so we basically give it some wheels
with these connector molecules, also of dynein.
So that allows us to have this assembly
that moves down the microtubule.
We have anterograde, moving away,
and retrograde, coming back. Transports.
So we can take stuff out in the cell and
we can bring stuff back.
Those molecular motors are slightly different from one another
but they essentially work in the same fashion.
So the interior network of cytoskeletal elements or
proteins that are cytoskeletal elements
are actually connected pretty well to an exterior network
of proteins that we call the extracellular matrix.
The place that they're most tightly connected
is at these proteins called integrins.
Those are the proteins that anchor many of the
cytoskeletal elements to the edge of the cell
in order to form more structure for that cell. These proteins
transfer across the membrane, they're transmembrane proteins
that also have domains on the outside of the cell.
And they are associated with other fibers like collagen
and elastin and glycoproteins and some other peptidoglycans
so that the cell has some sort of protection. Because you'll
recall animal cells don't have a cell wall like bacteria do
or plant cells do or fungal cells do.
And so this extracellular matrix's function is to
provide some degree of protection to the cell
as well as allow the cells to identify themselves.