Mitosis | Cells | MCAT | Khan Academy
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Mitosis | Cells | MCAT | Khan Academy

– In the previous video,
we talked about interphase which is the bulk of a
cell’s life cycle as it grows and its DNA replicates,
and it grows some more. And now, we’re gonna talk
about the actual cell division. We’re gonna talk about mitosis. And if you wanna be precise,
mitosis is the process by which this one nucleus
will turn into two nuclei that each have the original
genetic information. Now, as we exit mitosis,
we get into cytokineses which will then split each of the nuclei into a separate cell when
we split the cytoplasm right over here. We split or the cell as
it turns into to cells. Well, let’s see how all of this happens. So the first phase, and I’ll
leave the end of interphase right over here. We have this big cell, our
DNA has been replicated. We have two centrosomes right over here. The first phase of
mitosis involves the cell and I might draw a little
bit smaller just so I have enough space here. So, involve. So, this is the cell right over here. So we’re gonna go to this
phase right over here. And a few things start happening. One, the DNA, the chromosomes
go from being in their chromatin form where
they’re all spread out to kind of a more condensed
form that you can actually see from a light microscope. So for example, that magenta
chromosome which is now made up of two sister chromatids
after replication, we talked about that
in the interphase video. It might look something like this in a … It might look something like this if you were to look in a microscope. It’s unlikely to be magenta but
it’s gonna have kind of that classic chromosome shape
that you’re used to seeing in textbooks. And it has the centromere that connects these two sister chromatids. Right now, both of these two
sister chromatids combined are considered to be one chromosome. Even though before replication
it was still considered, the magenta stuff was still
considered to be one chromosome. And we can draw the blue chromosome. Once again, it’s now
in the condensed form. That’s one sister
chromatid right over there. That’s another sister chromatid. They are connected at the centromere. So they’re condensing now
as we enter into mitosis. And the nuclear membrane starts to go away. So the nuclear membrane
is starting to go away. And these two centrosomes
are starting to migrate to opposite sides of the cell. So one of them is going
over here and one of them is maybe going to go over here. So they’re migrating to
opposite sides of the cell. And it’s pretty incredible. It’s easy to say, “Oh, this
happens and then that happens.” Remember, this cell doesn’t have a brain. This is all happening through
chemical and thermodynamic reactions and the way, just
based on certain triggers of where the cell is and its life cycle. It’s amazing that this is happening. It’s amazing that the structures, and what sometimes we
consider to be a simple thing but it’s actually
incredibly complex thing. It kind of knows what to do even though it has no intelligence here. And a lot of what I’m talking about, the general overview of the
process is well understood but scientists are still
understanding exactly how do the different things
happen when they should happen and by what mechanism and
what’s actually happening. Sometimes, molecular or atomic basis. But anyway, this first phase of mitosis, the nuclear envelope, the nuclear membrane starts to disappear. The centrosomes migrate to
the opposite ends of the cell. And our DNA condenses into
kind of the condensed form of the chromosomes. And we call this prophase. Prophase. Prophase of mitosis. Now, in the next phase. In the next phase, let
me draw my cell again. Drawing that same green color. In the next phase, your nuclear membrane is now gone. And the chromosomes start lining up in the middle of the cells. So you have the blue one right over here, the blue one that’s one sister chromatid. Here’s another sister chromatid and they’re connected at the centromere, not to be confused with a centrosome. And then, here’s the magenta, one of the magenta sister chromatids and another one. And once again, it’s not
magenta in real life, I’m just making it a magenta
because it looks nice. That’s the centromere right over there. Our centrosomes are at opposite ends of the cell at this point. At opposite ends of the cell. And you might have heard of the word, let me label this again. I labeled it in a previous video. That’s centrosomes. Centrosomes where the two
sister chromatids are connected. That’s a centromere. Centromere. Now, you might heard
of the word centrioles. Centrioles are actually, they help, they are exist inside the centrosomes. They’re these two kind of
cylindrical looking structures. Each of the centrosomes
have two centrioles. But for the sake of
this video, you can say, “Well, the centrioles are
just part of the centrosomes.” But I’m just listing you all the words that involves centri something. Centrioles right over there
and you have two of them per centrosome. So hopefully, that helps
clarify some confusion. But these things line up. And a lot of what you’re about
to see, this orchestration, these things moving around
in the cell, things lining up and soon things pulling apart,
these are all coordinated with actually a fairly
sophisticated mechanism of kind of a scaffold of this kind of
ropes, these microtubules. And the centrosomes’ role, until now I’ve just been kind of drawing. I mean, what do they do? Well, the centrosomes’
role is these microtubules extend from them to each
other and to the centromeres of these chromosomes
and to a large degree, they’re not the only actors here. They help pull and push
things in the right way. So these help keep make sure
that the two centrosomes push away from each other. And then as we’ll see in the next phase, that they’re able to
pull one of each of the sister chromatids from
each of the pairs towards each of them. So this right over here where you see where the nuclear envelope
is now gone, the chromosomes have been lined up just like
this and your centrosomes are on opposite side of your cell. We call this the metaphase. We call this the metaphase of mitosis. And then you can imagine
what’s going to happen next. What’s going to happen next? What’s going to happen next is … Let me, I don’t wanna draw it
too big ’cause I wanna be able to fit it all in one page. What’s going to happen next is that those microtubules are
going to start pulling on each of the sister chromatids. Let me draw that. So you have this
centrosome right over here. You have all these
microtubules in your cell. You have the centrosome right over here, all those microtubules. And this one is going to be pulling, is going to be getting
one of the blue chromatids to pull towards it or to move towards it. So let me draw that. So this is one blue
chromatid right over here. aAd this one is going to
be pulling the other blue chromatid towards it. And same thing for the magenta. And same thing for the magenta. So that one’s being pulled to that way. And this one is being pulled that way. And just in case you’re
concerned about the, some of more of the words
of vocabulary involved, the point it was this
microtubules connect to what used to be sister chromatids, but now that they’re apart,
we now call them chromosomes. When they emerge, this is
one chromosome and they have two sister chromatids. But now they’re apart, we would
actually now consider this each an independent chromosome. So now, you actually have
four chromosomes over here. This point right over here,
we call it kinetochore. And even exactly how that interphase works and exactly how things move
is not fully understood. Some of this stuff is
understood but some of this is still an area of research. So something even as
basic as cell division, not so basic after all. So this right over here where
you can start to see the DNA kind of migrating to their
respective sides of the cell. We call this the anaphase. We call this the anaphase. And that takes us to the
last formal phase of mitosis and that is called telophase. Telophase. And in telophase, I’m gonna
do my best shot to draw it. And you could already see
I have started to draw that the cellular membrane is
starting to pinch in kind of in preparation for cytokineses,
in preparation for the cell splitting into two cells. So I’ll do it a little bit more. Cytokineses is usually described
as kinda being a separate process in mitosis although
it’s obviously they are, they kind of together
help the cell fully turn into two cells. So now in telophase, so you have this, what used to be a sister chromatid, now we can call it a
chromosome on its own. And we have this chromosome. And we have this chromosome right over there. We have to do it on both sides. So you’re there and you have this right over here. And actually, let me draw
it a little bit different. Because at this phase, you’re
really starting to unwind what happened at prophase. So prophase, you have the disappearance of the nuclear membrane and
you have the condensation of the chromosomes into this form here. Telophase, that’s unwinding a little bit. So actually, let me draw
the two centrosomes. So you have one centrosome
with that same color that I had before. So you have one centrosome right here. You have another centrosome
right over there. And now, the DNA, this blue DNA, this chromosome is now here
but it’s starting to get a little under wind a little bit, same thing on this side right over here. Magenta chromosome is
on here but once again, it’s starting to get a little bit unwound. Same thing over here. And you start to have
nuclear membranes forming around the DNA. So once again, it’s kind of redoing what was undone in prophase. Undone in prophase. And so, when you’re done, essentially, you’re gonna have these nuclear membranes. The DNA is gonna go back
to its chromatin form. And then you have cytokineses. And cytokineses is the process
by which this gets fully pinched together and you
have two separate cells. And some folks will say, “Oh,
it kind of begins in anaphase “and finishes after telophase.” But it’s kind of happening
near the end of mitosis in parallel with it. So this is cytokineses. Cytokineses. Cytokineses right over here. This essentially is how this larger cell that had two nuclei, how
this divides, fully divides into two cells. And at that point,
you’re back to this phase of the cell cycle. Now, each of these two cells are going to go through interphase, G1, S-phase replicate their DNA,
and G2 phase goes some more and then it go through mitosis again. And then these two will
turn into four cells. Anyway, hopefully, you enjoyed that.

About James Carlton

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100 thoughts on “Mitosis | Cells | MCAT | Khan Academy

  1. when people they put out this long presentations with so much info in them, they are hard to follow. they are all so worried about sounding academical and the message gets lost. but not with you. you are awesome.

  2. Thank you so much for going into all the details and explaining it! I really appreciate how much work you put into these videos!

  3. These videos make complex concepts so much easier to understand. Thank you so, so much! I can't believe how much I enjoy watching them. I choose them over my lectures any day! This is HEAVEN to the visual learner, which is the best way I learn!

  4. سبحانك اللهم وبحمدك نشهد ان لا اله الا انت نستغفرك ونتوب اليك

  5. this is the best video ever, very informative and FUN. saved my life in ap bio and now i love the color magenta. 10/10 would watch again and again. what a good time best teacher EVER!!!!

  6. Omg thank you for making these videos! I have a test on mitosis and meiosis tomorrow and it was super confusing but i totally get it now!

  7. Thank you very much for the video, I struggled to comprehend mitosis from textbooks and lessons but this was very well presented

  8. gr8 video. just one question. after the telophase, when does the chromosome return to it's scrambled original form or does it at all?

  9. Most of your videos have lots of unnecessary waste time and words. Also your organization is not helpful. Im sorry i feel like feedback is important.

  10. I think there should be another name for a "chromosome" when it is replicated into two sister chromatids (duosome?). This new entity is essentially two chromosomes lassoed together and yet we still refer to it as "a chromosome", which can be confusing for students when describing mitosis/meiosis.

  11. I just have one small doubt… what happens to all the organelles in the cell when mitosis happens? Do they disintegrate along with the nuclear membrane?
    However, your videos are extremely well depicted and a great way to study! Hope you keep up your good work!

  12. Thank you so much for these helpful videos! I'm a visual learner and I couldn't get through college without YouTube! Only thing, with this video, you didn't mention the Prometaphase stage, which I need to know for class…there are 5 stages to mitosis, not four. Still a helpful video.

  13. Thank you so much. Our school has to take standard tests to graduate and this helps so much. Now, off to Meiosis!

  14. Amazing video thank you 🙂
    If anyone is in the UK studying A-Level Biology you also need to know that animal cells cleve from the outside in, and plant cells cleve from the inside out, laying down platelets of cellulose. It was a question that came up on a paper a few years ago and caught people by supprise!

  15. Quick question. How come on this video you begin with only two chromosomes while in my text and other videos I've seen 3 or four chromosomes? Is it just an arbitrary amount when you draw it since there are 46 chromosomes, or do you draw them with only 2 here on purpose?

  16. You should have a podcast ! Thank you so much . You have no idea how many students around the world that are blessed because of you .

  17. what I learned from this video:
    chromosomes are not magenta colored
    centrosomes are not to be confused with centromeres

  18. just wow. Thank you very much . you explained v well. even you emphasized those things every time where we can confuse like centromere centosome etc . Literally i can say that with the 16 years education i always confused about chromosome form now you cleared the concept about chromatid that this is also called one copy of chromasome . Thank you very much. sometimes we confuse even with very little things but you also clear little things. This is my first time when i heared your lecture and became your fan

  19. Thank you keep up the awesome work. I feel so much more ready for my big test coming up having watched your videos.

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