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Today's topic is the cell cycle and mitosis. But before we get into the cell cycle and

mitosis, we want to be sure to talk about why these words are important and how they

relate to real life. So if I say the word cancer, this words probably means something

to you. Either you know somebody who has been diagnosed with cancer or you've heard about

it on the news. There's many different types of cancers but one thing they all have in

common is that they are caused by uncontrolled cell growth. That means, someone's own cells

grow out of control. Now, that doesn't mean that there aren't other contributing factors

for example for some cancers having genetic links, meaning it runs in the family, can

make someone more likely to develop it, or having excessive exposure to UV light for

some cancers. Those are risk factors that can increase your risk. But the main cause

of cancer is uncontrolled cell growth. That also means it's something that it is not contagious

and that it's something that anyone can develop.

You have to realize that all the cells in your body are very busy. And they're either

in one of two different phases. They are either in a phase called interphase and during interphase

they are just growing, replicating DNA, their doing their cell functions or they are in

mitosis. Mitosis is a fancy word that means they are dividing, they are making new cells.

If you think about the cell cycle, whether they are in interphase or mitosis, it's kind

of like a pie graph. They are spending about 90% of their time in interphase. Most of the

time cells are not dividing, most of the time they are in interphase, they are growing,

they're doing their daily cell functions and they are replicating their DNA. Most of the

time, not dividing. Now, depending on what kind of cell, it might do mitosis more or

less often; for example, your hair follicle cells, they do mitosis frequently which is

why your hair can grow up to half an inch every month. But other cells like for example

your brain cells, your neurons, some of them do not perform mitosis, which is why if you

have some type of major injury to the spinal cord or to the brain, sometimes those do not

heal very well because those cells do not replicate.

So mitosis is very important to generate new cells, which can help with growth and also

if you damage your cells. If you're walking down the street and you have some kind of

accident, and you skin your knee, well you're going to need to repair those damaged cells.

You're going to need to be able to mitosis to repair those cells. The thing is you don't

want your cells to be always doing mitosis because if their always doing mitosis, then

they are always dividing and then they're not carrying out their actual function and

that's a problem.

That's where check points come in handy. See, along the cell cycle there are check points

to check that the cell is growing correctly and replicating it's dna correctly and doing

everything it's supposed to correctly before it divides. And what happens if the cell fails

it's check point? The cell does something called apoptosis which basically means the

cell destroys itself, it self-destructs. This might seem kind of harsh but actually it's

really important because it ensures you don't have these cells that are messed up continue

on and divide. You don't want damaged cells to continue on and divide because they might

do not do what they are supposed to, they might start to grow out of control, they might

not be regulated correctly.

That's where cancer cells come in. See cancer cells, as we had said, are your body's own

cells that are growing out of control. So they are not following the rules of these

checkpoints, they are flying past the check points going through the cell cycle and frequently

doing mitosis, which means they are dividing very, very often. And so by doing that they

can grow into these things called tumors which are really a mass of cancer cells. So we're

not really sure what causes them to escape these check points. There are a lot of factors

that a person can have that will increase their risk of this happening, but when these

cells get past these check points and grow out of control, they become a problem. Because

many times they can travel through the bloodstream, they started growing out of control, the body

can't identify them and destroy them with the immune system and so this becomes an issue

and usually one the treatments that someone with cancer will go through is called chemotherapy.

And this works by targeting cells that go through the cell cycle quickly and hit mitosis

quickly. And that's one reason why many people will lose their hair when they are on chemotherapy

because their medication that's targeting fast growing cells and their hair follicle

cells are also fast growing cells.

Cancer cells have some other factors that make them difficult to treat. One is that

cancers have the ability to secrete their own growth hormone. This is very bad because

growth hormone in the sense, think of it as a hormone that says, "FEED ME." What happens

is the blood vessels will divert over to those cancer cells and supply the cancer cells with

nutrients. This is not good because it means the cancer cells will have the nutrients they

need to keep growing out of control. It also can take nutrients away from nearby healthy

cells. There are some medications that are being researched that maybe could stop the

growth hormone from cancer cells and in the sense that would be great because the cancer

cells would not be able to get the nutrients to grow out of control. Of course, you have

to make sure the medication is targeting just cancer cells and that hurting the growth hormone

of nearby healthy cells. You wouldn't want that. So it's kind of a tricky situation.

So let's recap what we talked about today. We talked about the cell cycle, how cells

are more frequently in interphase than in mitosis. Interphase is when cells are replicating

their DNA or their growing, and carrying out cell processes. In mitosis, the cells are

actually dividing. We talked about how during this cell cycle there are checkpoints that

regulate the cell and keep the cell from being able to continue on if it's damaged...unless

we're talking about cancer cells which are cells that have escaped the checkpoints and

are growing out of control. Be sure to check out our clip on mitosis. This process is really

fascinating, but it's also a really important one in order to understand how your body cells

work. That's it for the Amoeba Sisters, and we remind you to stay curious!