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