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Have you ever looked down at your leg or your arm to find some cut and you have no idea
where it came from or how you got it? So you put a band-aid on it and a few days later,
it's gone. It's all healed, and you don't even think anything of it of the amazing process
that causes this to happen. Or let's say your looking at your nails and you notice that
they are kind of jagged because they have really grown since the last time you cut them
or filed them down or let's say you look in the mirror and you notice that you are a lot
bigger than you were when you were five years old. What do all of these things have in common?
All of these things have one thing in common and that is mitosis.
Mitosis is a type of cell division done by most of your body cells and it's really important
for cells to divide. If they didn't divide, you wouldn't grow. I mean, how do you grow
if you can't make more cells, right? So, one reason why you're bigger than you were when
you were 5 is mitosis. Mitosis also is great for repair of damage. If you have some kind
of accident like when we were talking about the cut on your arm or leg you want to make
sure it can get repaired well you have to make more cells to do that. So mitosis is
great for that. What mitosis is not, it's really important to understand what it is
not, it is not a process that makes sperm or eggs cells, because that is something called
meiosis, which sounds like mitosis...unfortunately, but it is a different process. Mitosis is
only done by body cells.
Mitosis also makes identical cells, that is the goal, identical cells. So if you're trying
to make more skin cells, to replace worn out or damaged cells, you don't want to start
suddenly making stomach cells there. That would be ridiculous! You want to make sure
you have identical cells replacing what was lost, so mitosis makes identical cells. It's
a real important thing. Now, it's also important to understand that your cells are not dividing
all the time. If all they did was divide, it would just be rapid crazy growth. In fact,
it's kind of what cancer is. Cancer is uncontrolled cell growth. We have a great clip on the cell
cycle and what the cell is usually doing most of its daily life, which is actually a phase
called interphase where it's growing and replicating it's dna and carrying out its daily cell functions.
That's where it spends most of its time doing. But mitosis is a very short amount of time.
During that time, it's very important process because this is where it's going to divide.
Before we get into the steps of division, it's really important to understand that your
cells have something inside them -- an organelle called the nucleus. And the nucleus holds
your DNA. DNA is really important because it's your genetic information. And if you're
going to make more cells, you need to have the same DNA in those new cells as you did
in your original cells. You want it to be identical, no mistakes. Very important.
The problem is you've got a LOT of DNA. And we've got to get that DNA into the new cells
using mitosis. So there has to be a better way to organize that DNA, like that DNA needs
to go to the Container Store and get organized. Well, what actually happens is that DNA can
be organized into these units called chromosomes. Chromosomes are made of DNA and protein. You've
probably heard before that humans have 46 chromosomes, that means in human body cells,
in the nuclei, that's the plural of nucleus. You don't say nucleuses, you say nuclei. In
the nuclei, there are 46 chromosomes. So basically that means that DNA is organized in chromosomes;
it also makes it a lot easier to move over when you're making new cells.
Okay, now here is something that is tricky about mitosis that students get confused with.
So if you have 46 chromosomes in a cell, you have to duplicate those chromosomes, that
basically means your duplicating your DNA -- remember chromosomes are make of DNA and
protein -- you're duplicating the chromosomes before they divide. You have to do that because
if you're going to make an identical cell that has 46, well you have to duplicate it
before splitting. So if you look at our cell cycle video clip -- we talk about an interphase
which is a state that most of the time cells are in -- they actually duplicate their DNA.
So during that time, they would have duplicated DNA so instead of 46 chromosomes during interphase,
they would duplicate and have up to 92 chromosomes. So that when it gets to mitosis, they will
be able to split into two cells that each have 46 chromosomes and that will be identical
to the original cell.
So let's get right into the cell cycle. I like to tell students to remember PMAT. It's
a little acronym that helps you remember. The P is for prophase. The M is for metaphase.
The A is for anaphase. The T is for telophase. So remember: PMAT. That is the stages in order.
So the very first step is prophase. Prophase because it's the beginning step, the nucleus
is still there and it's going to go away in a little bit so this is a stage where it's
actually still there. And the chromosomes are visible; in fact, we say they're condensing
which means they are thickening and visible. So prophase very beginning step.
The next stage is metaphase. M for metaphase, but I also like to remember the M for middle
because in this stage the chromosomes line up in the middle of the cell. The nucleus
has been disassembled, it's no longer there so we've got the chromosomes in the middle
waiting up there to be pulled apart for the next stage.
Next the A is for anaphase. In anaphase, I like to think as the A is for "away." The
chromosomes move away, they are moving to the opposite side of the cell, so they are
kind of moving to the poles of the cells. What's happening now is that the cells are
going to split apart. Now one thing to point out, these chromosomes are not just moving
by themselves, they actually have something called spindles. These spindles are fibers
that help move the chromosomes to the ends. Kind of helps them move along.
The last stage the T is for telephase. In telephase, the chromosomes are actually at
the complete opposite ends and new nuclei are forming on each side to make these two
new cells. And they are starting to surround the chromosomes on both sides. So I like to
think the T is for "two" because in mitosis you end with two cells. And, again, remember,
they are identical.
You can really quiz yourself online with a lot of mitosis pictures. There's tons of mitosis
quizzes online to practice being able to look at a mitosis picture and naming what stage
it is. And remember we really do care about mitosis because without it we wouldn't understand
how cells grow, how they repair damage and, it's really a lot of our cancer research is
dependent on understanding mitosis. Cancer itself is uncontrolled cell growth - so in
other words, uncontrolled mitosis. Well, that's it for the amoeba sisters and we remind you
to stay curious.