Packaging of DNA: Eukaryotes - Molecular Basis of Inheritance, Biology, Class 12 Video Lecture

hello friends this video on molecular
basis of inheritance part 7 is brought
to you by exam feel calm no more fear
from exam let us now talk about it you
can use so now let us see how is the DNA
headings packed inside the nucleus in
case of eukaryotes now in prokaryotes it
is quite simpler when compared to that
in case of eukaryotes so what happens in
eukaryotes and eukaryotes there are some
special proteins which are present they
are positively charged and they are
basic in nature and these proteins are
known as histones on the stone proteins
whatever you call them now these
proteins are rich in amino acids and
these are minor acids are basic in
nature now as I mentioned before also
the DNA is negatively charged due to the
presence so of the negative phosphate
group and these proteins are positively
charged so obviously there will always
be an affinity between the DNA and these
positively charged histones now due to
this affinity let us see what happens
now DNA will wrap around the histone
octamer what is optimal
octa means 8 the world octa means 8 now
what happens is these histone proteins
they are exposed for proteins and eight
proteins grouped together to form a
histone octamer now DNA will wrap around
this histone octamer
and it will form a structure known as
new lee ozone so you see all the terms
are very similar to nucleus because they
are located inside the nucleus so this
is how a nuclear zone will look like so
this entire structure is a nucleosome so
here the red colored string which you
see the double-stranded structure that
is DNA and here you can see eight cube
and ball-like structure spheres each
sphere represents one histone protein so
total eight hit stone proteins will
group together to form the octamer and
the DNA will wrap around the octamer to
form a structure known as
nucleo zone so this capture is
nucleosome how is the structure warm
this
transform because the octamer was
positively charged DNA was negatively
charged so they got attracted towards
each other and that is our DNA wrapped
around them of Tamid okay
so now each nucleosome contains 200 base
pairs of the DNA helix so now you see
this is how it is going to like be
wrapping around the entire octamer so in
1 october it is seen that the entire DNA
which is present that contains around
200 base pairs i was telling in one of
the previous slides like that one one
turn or of the one turn of the helix
that is the pitch of the helix contains
just 10 base pairs so when you say 200
base pairs that means 20 turns of the
headings so maybe like this is one turn
again this is one turn so that is how
there will be some 20 terms of the DNA
which will be present in each nucleosome
now when we looked at it a tableau on a
broader level how does it look like so
in any mammalian cell the number of
nucleosomes is equal to the number of
this entire structure which you see here
right now it looks very big but actually
when you see it it is a very tiny
structure so when you observe it under
an electron microscope pigeons are quite
powerful microscope how do they the pure
you know they will appear like beads on
a stool so they'll appear as small as as
tiny as beads so this is how it will
look like so normally this is how the
chromatin looks like the red colored
structure right now if you observe it
under an electron microscope this is how
it will look like so each orange colored
structure which you see which appears
like a bit so this orange color
structure is nothing but a new Pew zone
so this orange color sphere is not a
single sphere but it is a histone
octamer
which is being wrapped around by DNA so
this is how the appearance and what is
this red
train this is nothing but the chromatin
so it'll delay chromatin and in between
you have the nucleosomes so this is how
DNA is packaged inside the nucleus now
you imagine it yourself now if DNA is
getting wrapped over something what is
happening it is like a thread it is a
long chain so you are actually wrapping
the chain over something so what has
happening you are actually decreasing
extent so when you wrap it over so many
nucleosome I mean over so many October's
what happens the length reduces a lot
and it becomes so compact that it fits
inside the nucleus and this is the
strategy of packaging the DNA inside the
nucleus so one nucleosome contains 200
base pairs so one nucleosome contains
200 base pairs and i already told you
that the total base pairs in any in a
typical mammalian cell is around 6 point
6 into 10 to the power 9 so this is the
total number of base pairs so what do
you think would be the total number of
nucleosomes in a mammalian cell so the
number of nucleosomes will be equal in 6
point 6 into 10 to the power 9 divided
by 200 so that is equal to 33 into 10 to
the power 6 so these many nucleosomes
will be present in a cell and each of
these nucleosomes will appear as a bit
and that is why the structure is offers
known as bits on string because
chromatin appears as string and new view
zones appear as beads so this is how DNA
is packaged inside the nucleus and these
chromatin later during cell division
they condense together to form the
chromosomes so now that we have
discussed about chromic and let us talk
about a few more important things about
chromatin now there are two forms of
chromatin one is you chromatin and the
other one is heterochromatin now why am
I suddenly discussing about the
different form
so chromatin is the coiling and
condensing of the chromatin actually
forms the chromosome and you all know
how much important chromosome is for the
process of inheritance okay so now here
we will see that during this condensing
I mean it when this condensation take
place in two chromosomes these
nucleosomes they are not present
everywhere somewhere they are more
somewhere they are less so that is why
we are discussing about euchromatin and
heterochromatin
so in euchromatin the DNA packaging this
loser so the DNA is packaged but it is
not very compactly or it is not very
densely packed so there are a lot of
empty spaces there so that region is
known as euchromatin so here in this
picture this is the picture of them
nucleus so where you can actually see
the nucleolus so this is the nucleolus
and here you have the chromatin so this
portion the yellow colored portion as
you move from Aten where you just see
being colored structure something it is
not very dense totally somewhere you can
see the pink colored structure and just
outside towards the paint very you have
the hetero from at anywhere you see a
lot of green colored structure so what
is that green structure that green
structure represents the presence of DNA
so you chromatin has looser DNA
packaging it is lightly stained when
observed under microscope
so this you chromatin sense it has
lesser amount of DNA when compared to
heterochromatin so it is lightly stained
when observed under microscope so
greater the amount of DNA more will be
the staining when observed under
microscope it contains less DNA
transcriptionally active so what do we
mean by transcriptionally active now
what happens is that for transcript
transcription
what does transcription first of all
well transcription is nothing but
creating RNA from DNA so in very grameen
i am just giving a very simple term to
explain what is transcription so if you
want to synthesize
from DNA that process will known we will
be called as transcription now for
transcription the that portion of the
genes need to interact with the proteins
so in this structure the regions are
accessible so those regions are
accessible and that is why it is
transcriptionally active but when you
talk about heterochromatin there the DNA
is packaged in a very tight race a lot
of DNA is present there it contains more
DNA so it is directly stained when
observed under microscope it has more
DNA and it is transcriptionally inactive
that means that portion of the
DNA which needs to be exposed in order
to synthesize RNA that is hidden here
because like what happens is if you have
too much of DNA so what happens if it is
very much compact so what happens that
portion of the DNA which needs to be
exposed for transcription that doesn't
happen and that is why it is
transcriptionally inactive so the
regions the appropriate regions needed
for transcription they are in accessible
and therefore transcription is inhibited
therefore it is said that
heterochromatin is transcriptionally
inactive but you chromatin is
transcriptionally active but when you
talk about the DNA content
heterochromatin has more DNA and you
chromatin has less DN u chromatin is
found in both eukaryotes as well as
prokaryotes whereas heterochromatin is
found only in eukaryotes and prokaryotes
you do not have heterochromatin so this
was about the different forms of
chromatin now these chromatin condensed
to form chromosomes during cell division
now again during the condensation of the
chromatin to form chromosomes what who
helps during that time again some
protein cell and those proteins are
known as the non-histone proteins or
non-histone chromosome proteins so the
proteins which help the DNA to package
itself that is called the histone
proteins and the proteins which help the
chrome
adding to condense further to form
chromosomes they are the non-histone
chromosome proteins on NHC proteins so
that is also another name n8z
non-histone chromosome proteins thank
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