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  • Every human being starts out the same way:

  • two cells,

  • one from each parent,

  • found each other and became one.

  • And that one cell reproduced itself,

  • dividing,

  • and dividing,

  • and dividing

  • until there were 10 trillion of them.

  • Do you realize there are more cells in one persons body

  • than there are stars in the Milky Way?

  • But those 10 trillion cells are not just sitting there in a big pile.

  • That would make for a pretty boring human being!

  • So what is it that says a nose is a nose,

  • and toes is toes?

  • What is it that says this is bone,

  • and this is brain,

  • and this is heart,

  • and this is that little thing in the back of your throat

  • that you can never remember the name of?

  • Everything that you are or ever will be made of

  • starts as a tiny link of instructions

  • found in each and every cell.

  • Every time your body wants to make something,

  • it goes back to the instruction book,

  • looks it up, and puts it together.

  • So how does one cell hold all that information?

  • Let's get small.

  • I mean, really small,

  • smaller than the tip of a sewing needle.

  • Then we can take a journey inside a single cell

  • to find out what makes up the book of you,

  • your genome.

  • The first thing we see is that the whole genome,

  • all your DNA,

  • is contained inside its own tiny compartment

  • called the nucleus.

  • If we stretched out all the DNA in this one cell

  • into a single thread,

  • it would be over 3 feet long!

  • We have to make it fit in a tiny compartment

  • that is a million times smaller.

  • We could just bunch it up like Christmas lights,

  • but that can get messy.

  • We need some organization.

  • First, the long thread of DNA wraps around proteins

  • clustered into little beads called nucleosomes,

  • which end up looking like a long, beaded necklace.

  • And that necklace is wrapped up in its own spiral

  • like an old telephone cord.

  • And those spirals get layered on top of one another

  • until we get a neat little shape that fits inside the nucleus.

  • Waaah! Three feet of DNA squeezed into a tiny compartment.

  • If only we could hire DNA to pack our suitcases!

  • Each tiny mass of DNA is called a chromosome.

  • The book of you would have 46 chapters,

  • one for each chromosome.

  • 23 chapters of your book came from your mom,

  • and 23 chapters came from your dad.

  • Two of those chapters, called "X" and "Y",

  • determine if you are male, "XY",

  • or female, "XX".

  • Put them together and we get two almost identical

  • but slightly different sets of 23 chapters.

  • The tiny variations are what makes each person different.

  • It's estimated that all the chapters together

  • hold about 20,000 individual instructions, called genes.

  • Written out, all those 20,000 instructions

  • are 30 million letters long!

  • If someone were writing one letter per second,

  • it would take them almost an entire year to write it once.

  • It turns out that our genome book is much, much longer

  • than just those 30 million letters,

  • almost 100 times longer!

  • What are all those extra pages for?

  • Well, each page of instructions has a few pages of nonsense inserted

  • that have to be taken out before we end up with something useful.

  • The parts we throw out, we call introns.

  • The instructions we keep, we call exons.

  • We can also have hundreds of pages in between each gene.

  • Some of these excess pages were inserted

  • by nasty little infections in our ancestors,

  • but some of them are actually helpful.

  • They protect the ends of each chapter from being damaged,

  • or some help our cells find a particular thing they are looking for,

  • or give a cell a signal to stop making something.

  • All in all, for every page of instructions

  • there is almost 100 pages of filler.

  • In the end, each of our books' 46 chapters

  • is between 48 and 250 million letters long.

  • That's 3.2 billion letters total!

  • To type all that copy, you would be at it for over 100 years,

  • and the book would be over 600,000 pages long.

  • Every type of cell carries the same book,

  • but each has a set of bookmarks that tell it exactly

  • which pages it needs to look up.

  • So a bone cell reads only the set of instructions it needs to become bone.

  • Your brain cells,

  • they read the set that tells them how to become brain.

  • If some cells suddenly decide to start reading other instructions,

  • they can actually change from one type to another.

  • So every little cell in your body is holding on to an amazing book,

  • full of the instructions for life.

  • Your nose reads nose pages,

  • your toes read toes pages,

  • and that little thing in the back of your throat,

  • it's got its own pages too.

  • They are under uvula.

Every human being starts out the same way:

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B1 TED-Ed dna tiny dividing genome bone

【TED-Ed】DNA: The book of you - Joe Hanson

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    VoiceTube posted on 2013/05/06
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