00:00:13
Every human being starts out the same way:
00:00:16
one from each parent,
00:00:17
found each other and became one.
00:00:19
And that one cell reproduced itself,
00:00:24
until there were 10 trillion of them.
00:00:26
Do you realize there are more cells in one persons body
00:00:28
than there are stars in the Milky Way?
00:00:32
But those 10 trillion cells are not just sitting there in a big pile.
00:00:35
That would make for a pretty boring human being!
00:00:38
So what is it that says a nose is a nose,
00:00:40
and toes is toes?
00:00:41
What is it that says this is bone,
00:00:43
and this is brain,
00:00:44
and this is heart,
00:00:45
and this is that little thing in the back of your throat
00:00:47
that you can never remember the name of?
00:00:49
Everything that you are or ever will be made of
00:00:51
starts as a tiny link of instructions
00:00:53
found in each and every cell.
00:00:55
Every time your body wants to make something,
00:00:56
it goes back to the instruction book,
00:00:58
looks it up, and puts it together.
00:01:01
So how does one cell hold all that information?
00:01:04
Let's get small.
00:01:05
I mean, really small,
00:01:06
smaller than the tip of a sewing needle.
00:01:08
Then we can take a journey inside a single cell
00:01:10
to find out what makes up the book of you,
00:01:14
The first thing we see is that the whole genome,
00:01:17
is contained inside its own tiny compartment
00:01:19
called the nucleus.
00:01:20
If we stretched out all the DNA in this one cell
00:01:22
into a single thread,
00:01:23
it would be over 3 feet long!
00:01:26
We have to make it fit in a tiny compartment
00:01:27
that is a million times smaller.
00:01:30
We could just bunch it up like Christmas lights,
00:01:32
but that can get messy.
00:01:34
We need some organization.
00:01:35
First, the long thread of DNA wraps around proteins
00:01:38
clustered into little beads called nucleosomes,
00:01:40
which end up looking like a long, beaded necklace.
00:01:43
And that necklace is wrapped up in its own spiral
00:01:45
like an old telephone cord.
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