And then we are able to move into; Keep in mind these
aren't one phase, the next phase, the next phase.
It's a very dynamic process. We've just sort of
divided them up to make it easy to understand
what's happening and describe some landmark events.
So in prometaphase, we see a few other things
happening as we prepare for cell division. We'll
see that the mitotic spindle begins to form.
The kinetochore microtubules which come from the
centrioles will connect to the kinetochore handles
on each of the sister chromatids. And they'll
start jostling and moving the chromosomes around
getting ready to line them up in the
center of the cell for cell division.
Then we will see that during metaphase, the
kinetochore microtubules finally pull them into place
along the central line of the cell.
So looking a little more closely at that. We see
during metaphase the individual replicated
chromosomes with their sister chromatids are paired
because they're stuck together by those cohesin
proteins. They're paired right on the central line
of the cell. The central line of the cell
is called the metaphase plate. It doesn't physically
actually exist. It's just the central line of the cell.
So the metaphase plate is just the area that the
chromosomes line up upon. And in addition now we see
another set of microtubules. So we have the kinetochore
microtubules grabbing onto the handles on the sides of
each chromosome and they are getting ready to pull
them apart. But in addition these polar
microtubules are coming from the poles of the cell
and they actually line up on each other and they're
polymerized to grow and grow and grow and grow and
actually push the cell longer. So you have two
things going on. Polar microtubules pushing the cell
longer. Kinetochore microtubules attaching to the
kinetochore handles on the sister chromatids, getting
ready to pop them apart. And that happens
when we enter anaphase. So anaphase, as we take a
closer look, we'll see that the sister chromatids
are separating. Now, we are going to revert to a
little language lesson here because it is really
important to note that these are no longer considered
sister chromatids. Chromatids are only chromatids
when they are attached to each other with those
cohesin proteins right at the centromere.
Once they become unattached during anaphase, they
are now daughter chromosomes. They're chromosomes
of their own device now. So their going to be packaged
into their own cells. So they are full on adult
chromosomes. Let's think of it that way. So, a little
closer look at the details here. We see that
the cohesin proteins break down. The sister chromatids
are able to pull apart. The kinetochores pull them
longer. The polar microtubules push the cell longer.
Kinetochore microtubules are shortening pulling
the sister chromatids which are not sister chromatids
anymore. They are daughter chromosomes.
Pulling them to the poles of the cell. Now the poles
are going to pull apart in anaphase.
They are moving apart from each other so
we'll see elongation of the cell.