Molecular Visualizations of DNA - Original High Quality Version

- [Narrator] In this animation,

we'll see the remarkable way
our DNA is tightly packed up

so that six feet of
this long molecule fits

into the microscopic
nucleus of every cell.

The process starts when DNA

is wrapped around special protein
molecules called histones.

The combined loop of DNA and protein

is called a nucleosome.

Next, the nucleosomes are
packaged into a thread.

The end result is a
fiber known as chromatin.

This fiber is then looped
and coiled, yet again,

leading, finally,

to the familiar shapes
known as chromosomes,

which can be seen in the
nucleus of dividing cells.

Chromosomes are not always present.

They form around the time cells divide,

when the two copies of the
cell's DNA need to be separated.

Using computer animation
based on molecular research,

we are now able to see how DNA

is actually copied in living cells.

You are looking at an assembly line

of amazing, miniature,
biochemical machines

that are pulling apart
the DNA double-helix

and cranking out a copy of each strand.

The DNA to be copied enters

the production line from bottom-left.

The whirling, blue molecular
machine is called helicase.

It spins the DNA as fast as a jet engine,

as it unwinds the
double-helix into two strands.

One strand is copied continuously

and can be seen spooling off to the right.

Things are not so simple
for the other strand

because it must be copied backwards.

It is drawn out repeatedly
in loops and copied,

one section at a time.

The end result is two new DNA molecules.