癌症 (英)

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癌症 (英) : 癌症是什麼，以及它為何是DNA複製錯誤所造成。

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Most cells in the human body just go about their
business on a daily basis in a fairly respectable way.
Let's say that I have some cell here.
This could be maybe a skin cell or really any cell in
any tissue in the body.
As that tissue is growing or it's replacing dead cells
the cells will experience mitosis
and replicate themselves
make perfect copies of each other.
And then those two maybe will experience mitosis
and then if they realize that, gee, you know
it's getting a little bit crowded.
There are other cells in my neighborhood.
They'll recognize that, and say, you know, I'm going to
stop growing a little bit.
That's called contact inhibition.
And so they'll just start growing.
And then let's say
one of them experiences a little defect,
and he says, you know what, gee,
something's a little bit wrong with me.
I, the cell, recognize this in myself, and the cells will
actually kill themselves.
That's how good of cellular citizens they are.
They'll kind of make way for other healthy cells.
So this guy might even kill himself if he realizes that
there's something wrong with him.
There's actually a cellular mechanism that does that
called apoptosis.
And I want to make this very clear.
This isn't some type of outside influence on the cell.
The cell itself recognizes that it's somehow damaged
and it just destroys itself, so apoptosis.
So that's the regular circumstance even when there
is a mutation.
And just to give you an idea, even if mutations are
relatively infrequent.
And I don't know the exact frequencies at
which mutations occur.
I suspect it's of different frequencies in different types
of tissues.
There are on the order of 100 billion.
Let me do it in a different color.
There are on the order of 100 billion
new cells in the human body per day.
So even if a mutation only occurs one in a million times,
you're still dealing with roughly 100,000 mutations, and
maybe most of the mutations, maybe they're just some little
random things that don't really do a lot.
But if the mutations are a little bit more severe, the
cell will recognize it and destroy itself.
And I want to make a very clear point here.
I'm talking about the cells of the body or most of the body.
These could be cells in my eyes
or the cells in my brain or the cells on my leg.
These aren't my germ cells.
So these mutations, even if the cell survives
will not be passed on to my offspring.
That's an entirely different discussion when
we talk about meiosis.
These are all my body cells and they're replicating, and
we've gone over this with mitosis.
So any mutations here, they'll either do nothing, or the
cells might malfunction a little bit, or the cells might
hurt themselves or hurt me, but they're not going to
affect my offspring.
And I want to make that point very clear.
Now, you're saying, hey, Sal, 100 billion new cells a day?
That must mean like every cell in my body has created, well
that just gives you an idea of how many cells we have. We
actually have on the order of, and you know it's obviously
not an exact number, but actually in the human body,
there's on the order of 100 trillion cells.
And if you look at it that way, you say on average, one
thousandth of your cells replicate each day, but the
reality is some cells don't replicate that frequently at
all and some cells replicate much more frequently.
Just to take a little side note here, this gives you an
appreciation, I think, for the complexity of the human body.
I mean we think of our own world economy and world
society as so complex, it's made up of 6 billion humans.
We're made up of 100 trillion cells.
Let me rewrite 100 trillion in billions.
100 trillion can be rewritten as 100,000 billion cells.
And each one of those 100,000 billion cells are these huge--
I know I shouldn't use the word huge-- but they're these
complex ecosystems in and of
themselves with their nucleuses.
And we'll talk about all the different organelles they
have, and we talked about cellular replication, DNA
replication and how the cell replicates.
So these things aren't jokes and they have all of these
complex membranes that take things into them.
They are creatures to themselves, but they live in
this complex environment or society that is each of us.
So that's just a side note just to appreciate how large
and how complex we are.
But you can imagine, and this is how I got off on this
tangent, if we're making on the order of 100 billion new
cells every day, you're going to have a lot of mutations,
and maybe some of the mutations, you know I said
some of them don't do anything.
Some of them, the cell recognizes that the cell is
just going to be kind of dead weight so the cell kind of
eliminates itself.
But every now and then, you have mutations where the cell
doesn't eliminate itself and it also deforms the cell.
So when you have that, let's say I have some cell here.
I have some cell and it's got some mutation.
I'll do that mutation with a little x right here.
That's in its DNA.
Maybe it's got a couple of mutations.
So one of the mutations keeps it from experiencing
apoptosis, or destroying itself, and maybe one of the
mutations makes it replicate a little bit
faster than its neighbors.
So this cell, through mitosis, it makes a bunch of copies of
itself or a ton of copies of itself.
And this kind of body of cells that essentially has a defect,
they're all from one original cell that kept duplicating and
then those duplicating, but all these are defective cells.
If you were to look at them compared to the tissue around
it, it would look abnormal in some way.
Maybe it wouldn't function properly.
This is called a neoplasm.
Now, a lot of neoplasms, well they don't have to
form a body like this.
Sometimes they might somehow circulate in the body, but
most of the time they form this kind of big lump.
And if they get large enough, they're noticeable.
And that's when we call it a tumor.
So if this is actually a lump of kind of differentiated
tissue that's definitely abnormal, that's
what you call a tumor.
So the term neoplasm and tumor are often used
interchangeably.
Tumor is the word we use more in our everyday vocabulary.
Now, if this lump just kind of grows to a certain size, it's
just there, it doesn't really do anything dangerous, it's
not replicating out of control.
I guess it's not replicating a lot faster than its
neighboring cells and it's just hanging out, maybe
growing a little bit, but not in any significant way harming
our environment, we call that a benign
tumor or a benign neoplasm.
And benign essentially means harmless.
Benign tumor.
That means that's good.
You want to hear that.
If you got a lump-- God forbid you have a lump either way--
but if you do and it's a benign tumor, that means that
lump, it can kind of stick around, no damage done.
But if these DNA mutations, and maybe some of these are,
it is benign, but maybe one of the benign ones has another
mutation in it that starts making it grow like crazy.
And not only does it grow like crazy,
but it becomes invasive.
And invasive means that it doesn't care what's
going on around it.
It just wants to infiltrate everything.
So let's say that guy grows like crazy.
Let me do it in a different color.
And he starts infiltrating other
tissue, so he's invasive.
So super growth, he's invasive.
So he doesn't care what's going on.
He's all of a sudden turned into some type of a cellular
psychopath.
And even worse, his descendants, it's not just one
cell anymore.
He just keeps duplicating and passing on this kind of broken
genetic information that makes it want to replicate.
And then maybe there could be more and more things that
break down in its I guess offspring or the DNA that
comes from its replications.
And actually, that's a good likelihood, because the same
parts of its DNA that broke down, some of the DNA that
broke down in this guy, some of the mutations might have
actually hurt the DNA replication scheme, so that
mutations become more frequent.
So more frequent mutations.
So as these replicate, more and more mutations appear, and
then maybe eventually one of the mutations appears that
allows these cells to break off and then travel to other
parts of the body.
And then those parts of the body start to take over and
start taking over all of the cells.
And this process is called the cell has-- this is one of the
hardest words for me to say, something wrong with my
brain-- but the cell has metastasized.
You might have heard the word metastasis, and that's just
the notion of these run amok cells all of a sudden being
able to travel to different parts of the body.
And I think you guys know what we call these cells.
These cells that aren't respecting their cellular
neighborhood.
They're growing like crazy.
They don't experience that contact inhibition.
They're invasive.
They start crowding out other cells and
hogging up the resources.
And they keep mutating really fast because they have all of
these genetic abnormalities.
And eventually they might even break away and start
infiltrating other parts of the body.
These are cancers or cancer cells.
And so you might have an appreciation for
why this is so hard.
Cancer is such a hard disease to quote, unquote, cure.
Because it really isn't just one disease.
It's not like one type of bacteria or one type of virus
that you can pinpoint and say let's attack this.
Cancer is a whole class of mutations where the cells
start exhibiting this fast invasive growth and this
metastasis.
So you might look at one type of cancer and be able to say,
hey, let's target the mutation where the cells look like this
and you're able to knock out some of them.
Let me do this in this color.
So maybe you're able to knock out that guy,
that guy, that guy.
But because their DNA replication system might be
broken in some way, they continue to mutate, so
eventually you have one version that's able to not be
knocked out by whatever method you get.
And so you have this kind of new form of cancer, and then
that new form of cancer is even harder to kill.
So you can imagine that cancer is kind of a
never ending fight.
And you kind of have to attack the general idea behind it.
Chemotherapy and radiation, all of these type of things.
They try to attack things that are fast growing because
that's the kind of one common theme
behind all of the cancers.
And we could do a whole playlist on what cancer is and
how people are attacking it, but I wanted to at least show
you in this video that cancer really is just a byproduct of
broken mitosis, or even more specifically, broken DNA
replication.
That we have all of these cells replicating themselves
every day on the order of 100 billion, and every now and
then something breaks.
Usually when they break, either nothing happens or the
cell kills itself.
But every now and then, the cells start replicating even
though they're broken.
And sometimes they start replicating like crazy.
If they just replicate, but they're really not doing any
harm, it's benign.
But if they start replicating like crazy, taking over
resources and spreading through the body, you're
dealing with a cancer.
So hopefully, you found that interesting.
You already know a good bit of the science that kind of deals
with what is probably one of the worst ailments that we
deal with as creatures.
I mean, obviously, we're not the only people who can
experience cancers.
Even plants have cancers.