hey guys let's take a look at some more
stuff on Nanome today let's pull up our
loading menu and let's take a look at a
nucleosome so last time we looked at
DNA and now we want to understand a
little bit better how DNA is packaged in
the cell so in the in the biochemistry
series we did talk about nucleosomes
quite a bit the way that DNA wrap around
histones as we can see here and it's
just great to be able to visualize this
a little bit more accurately so we can
clearly see the DNA with the backbone in
green and then the proteins we see all
those alpha helices so I and J here
are going to be our two complimentary
DNA strands so there's one and then
there's the other and we can even
highlight individual
nucleotides here and we can see those
being highlighted and as we scroll
through it's important to see that there
are a hundred and forty-six
nucleotides or base pairs total right if
we go 146 and 292 so that's 146 base
pairs of DNA in this nucleosome and
then as we said these are going to be
wrapped around these histones and so
there are eight histone proteins and we
can highlight them one by one so here's
the second one and so there are four
different proteins but there are two
copies of each so that makes this octameric disc and we can go ahead and look
at these one at a time all of these
proteins do have three alpha helices so
those are the red ribbons that we're
seeing and so all of the histone
proteins do have very similar structure
though there are slight differences like
this one has this this section
projecting outwards but on the whole
they're very similar and they form this
octameric disc we can take a look at
each one continuing here and that is
essentially the structure of the octameric
disk of histone proteins so once
again a nucleosome is just these
histone proteins and then the DNA that
wraps around them and so that is the
essential structure
of the nucleosome and so there's a lot
of other things that we can do here if
we want to get a little bit of a better
sense of the way this looks we can zoom
in a little bit and one thing we can
also do why don't we why don't we get a
sense of the the size of this thing here
right so we know that we can measure
distances with this tool and so let's
just let's go all the way across here
let's see what this what the dimensions
are from one end to another so we let's
zoom in a little bit so we can see what
we just did and it looks like from one
edge to the other we've got about 118
angstroms or 11.8 nanometers so it looks
huge but of course compared to
macroscopic objects it's still
completely invisible so let's get rid of
that and so that gives you an idea of
the scope of the nucleosome and of
course there are many many many of these
in a row which then supercoil to to
form chromatin and so that's that's what
this looks like and we can we can again
talk about how much DNA is being wrapped
around but I find it's nice to get a
sense of this thing if we just make it
real big and kind of fly through it
that's another way to look at it
sometimes we like to make it very small
and look at the whole thing but it's
it's very interesting to sort of fly
through this whole structure and feel
what it would feel like to be the size
of an atom so here we go and we're about
through to the other side so that is
what it would feel like to be inside a
nucleus own so a couple more things
about this we did say that there are a
hundred and forty-six base pairs
associated with this nucleus oh and in
terms of the number of turns there's
going to be about 1.6 to 1.7 turns so
starting here at the the free end we can
start going around and around and around
and then we will cross up over into this
second section here and all in all once
we get to the end the 146 base pairs or
to span about 1.6 turns around
after which it will then connect to the
next nucleosome and just will get a
bunch of these in a row which once again
supercoiling
the further supercooling will give us
our chromatin which is how it looks in
the cell so we can look at this a few
other ways I just turned ribbons off so
you know once again those ribbons on the
DNA backbone and on the alpha helixes
those are just formalisms sometimes it's
useful to just take a look at this
without those ribbons and just see all
the atoms and bonds and that's what that
would look like and so that's one
interesting way to look at this we can
also turn off the atoms and bonds and
just leave the ribbons because that
gives us sort of a different sense
remember all of these are
representations even the ball-and-stick
it's just it's one way of imagining or
visualizing it just like these ribbons
so none of them are completely accurate
but if we if we use a bunch of different
ways of visualize visualize this at at
different times we can you know get a
better sense of the reality of the
situation so there's that and we can
even we can even turn the surface on so
this gives you sort of a space-filling
model and the influence that this has on
its surroundings in terms of electron
clouds so that's a little bit about
nucleosomes a few different ways of
visualizing it and then a few different
facts about them so stay tuned for next time
