And then the elongation continues as we move into
telophase. I think about 'teloscope', telescope.
And separating of those two nuclei. So, now it's time
to repack the chromosomes into a nuclear envelopes.
During telophase, the goal is to get the new daughter
chromosomes into their own nuclei. In which case
we need to break down the spindle apparatus in order
to create a new nuclear envelope for each of the new
daughter nuclei containing daughter chromosomes. And
so as those nuclear envelopes form, the chromosomes
begin to unwind so that soon after we complete cell
division the DNA is available to make proteins
and have the cell function as normal cell would. So
then we have the organelles dividing between the cells.
And this is a pretty important phase. Telophase, we're
forming the new nuclear envelopes but now we need to
put some of the organelles in each end. We talked
about mitochondria having their own DNA.
So naturally mitochondria have to replicate
themselves also during this process.
In order for each cell to have mitochondria, we want
to have some ribosomes in each. So on and so forth.
So all of those organelles need to divide
before we actually have cytokinesis.
So, here is sort of a critical point. We've managed
to get our way through each of the phases of mitosis.
There are some distinct things that happen here.
To review, first of all it all makes sense.
We have to get the nuclear envelope out of the way.
We have to get microtubules in place to pull
sister chromatids apart. We have to have microtubules
to push the cell longer. And then eventually we
break those apart and we put them in new nuclei.
We've now got two separate nuclei and mitosis
is complete. But, we have one cell membrane still.
We've partitioned the contents of the cell,
the other organelles. But now it's time to look at
actual cell division. Cytokinesis is technically
not part of mitosis because mitosis by definition
is nuclear division whereas cytokinesis is
division of the cytoplasm or division of the cell
itself. So during cytokinesis, we're going to see a
belt of those fibers that are actin fibers in the cell.
The cytoskeletal elements. This is one of those
places they come into play. Pinching right down the
center of the cell. And because the membrane is very
fluid, we can pinch tighter and tighter and tighter.
Those actin molecules can contract and eventually
pinch off the cell so that we have two separate cells.
These are now the daughter cells. But again,
mitosis, nuclear divisions. Cytokinesis is division
of the cytoplasm. So now that we have our cells divided,
I think that you can have a great understanding of
the language of chromosomes. That's going to be
really important to pay specific attention to. I
might take a moment to write those terms down
because they are going to come up again when we look
at meiosis or the formation of gametes, sperm and eggs.
We are also going to be able to describe how
chromosomes are packed. Chromatin winds up into
tightly formed DNA so that we can move them nice and
neatly. I think of that as like winding up balls
of yarn so that you don't have to pull the spaghetti
apart. And then you are going to be able to diagram
each of the phases of mitosis. I don't think it's so
important to memorize the steps as it is to draw
the cell and think about where things need to be.
It's a fluid process. We divide into phases again for
landmarks. And then finally, you should really be able
to know the difference now and tell someone the
difference between mitosis and cytokinesis. Thank you
again for taking time to watch this lecture.
I look forward to seing you in the future lectures.