Polynucleotide Formation Video Lecture - NEET

hello friends this video on molecular
basis of inheritance part 3 is brought
to you by exam for your calm no more
fear from exam so the question is how
nucleotides join together to form
polynucleotide so we saw the three
different components which form one
nucleotide but the question is how are
these components connected to each other
now the nitrogenous base which we spoke
about just now I said right that they
can be purines and pyrimidines
so these nitrogenous bases are linked to
the pentose sugar through a n glycosidic
bond to form a nucleoside okay so two
important terms here so basically this
sugar is what pendo sugar any sugar is
going to be a carbohydrate so this
carbohydrate will join to this base
through a glycosidic bond now I am NOT
going to talk about each of these bonds
in detail because we have already spoken
about these in the lesson called by more
roots in class 11 so in case you want to
know these details you can refer the
lesson on biomolecules now see something
like this this let us suppose this is a
base so which is this purine or
pyrimidine yes exactly it is a pyramid
and why because it doesn't have you can
tell this very quickly because it
doesn't have a double ring structure
wherever you have a double ring
structure it can be a purely but
otherwise because of pyrimidine so this
pyrimidine base will get connected to
the sugar now the sugar again can be a
guy goes on a deoxyribose so this sugar
which you see on the screen whether it
is ribose or deoxyribose when it is
written there so it is easier for you to
tell but you can see here that among
oxygens less 21 oxygens there are the
oxygen has been removed so that is why
it is deoxyribose so this is deoxyribose
sugar so this sugar and this base will
get joined by a glycosidic bond now how
is that bond form so this bond is formed
by hydrolysis that is by removal of a
water molecule which is often known as
condensation right so this water
molecule is removed and
bond is formed between this nitrogen and
this hydrogen so that is how the
glycosidic bond formation will take
place so here you can see in this
picture so this is the sugar this
portion is the sugar this is the base
database is not being shown here so this
is the base and they are directly joined
here and then joining is due by the
hydrolysis of water removal of this
water and a bond formation take place
now this structure which is formed sugar
plus base this structure is known as
nuclear site and what are we talking
about we are talking about nucleotide so
when the sugar and the base combines
they form a nucleoside when the
nucleoside combines with the third
component that is the phosphate group
then a nucleotide is formed right so
nucleoside plus phosphate groups form
nucleotide so now a phosphate group is
linked to the 5 o h of a new blue side
through phospho ester bond to form a new
kind now first of all where is this 5 o
h now as per the rules of Norman clay
Chur in your chemistry you know right
the carbon atoms are numbered so here if
you see the carbon atoms are numbered in
this way 1 2 3 4 5 so here if you talk
about the ohq there is one Oh H which
was attached to the carbon one so at one
position this Oh H was connected so this
was 108 however this was used up during
hydrolysis for the formation of
glycosidic bond there is another Oh H at
the 3 position so how do we denote these
position is a 3 prime 5 prime or 1 prime
that is how we denote them and there is
another Oh H at the 5 in first position
of the carbon atom so that is
Prine orange now with this OAH another
bond is formed between the phosphate
groups and phosphate group comes
somewhere here so this is the phosphate
group so again with this phosphate group
a bond formation
take place then this point is known as
the fast food that is fosco ester bond
now why was this called glycosidic bond
because it was formed with the
carbohydrate and carbohydrate is also I
mean glucose is one of the common
example of carbohydrates so from there
it got its name like positive here it is
formed with the phosphate group so the
name is false for mr. bond
and here the bond formation will take
place again as a result of condensation
so you can see the same bond formation
ch2 this Oh H is gone this H is gone so
it will directly combined with O so this
is the bond formation here which has
taken these so what is this bond this
bond will be the phospho Eastern
bond and what was this one this bond was
the climb hosted bond right so now this
entire structure which is formed what is
it so this entire structure which is
formed is a nucleotide so this is just
one nucleotide but when you talk about
the structure of a DNA or the structure
of an RNA they are poorly nucleotides so
they have multiple such nucleotides
which are linked to each other
so again when multiples actually you
tides are linked to each other again a
bond is required to join one you unite
to another right okay so let us see how
that is done now multiple nucleotides
join together through 3 5 phosphodiester
bond so this is the bond which connects
the multiple nucleotides to form a poly
nucleotide so this poly nucleotide will
be a chain kind of a molecule like how I
was telling let us suppose if this is
one nucleotide this is not a nucleotide
this is another and you
this is yet another new blue light so
you can think of it like a train ever
you have in a train what do you have you
have different bogies or whatever you
call them compartments right so let us
suppose if if you join some 50
compartments together you get a real
long train so that is how it is here if
you join multiple nucleotides one after
another you get a chain of a poly
nucleotide and this is how the structure
is for RNA and DNA so now let us see how
exactly is this phosphodiester bond
formation taking place see this is how
it loose so each of this structure is a
nucleotide it has the phosphate group it
has the sugar it has the base so this is
one nucleotide again this is another
nucleotide this is the third nucleotide
now these nucleotides has to be joined
together so how will they join so let us
see so this is how the bond formation
intake is taking place so if you see
here this phosphate group here this
phosphate group had a free open share
right
similarly this phosphate group again had
a free Oh a chip so the bond formation
actually take place with this phosphate
group and this sugar so the sugar of the
first nucleotide the bond phosphodiester
bond formation takes place between bunch
the sugar of the first nucleotide and
the phosphate group of the second
nucleotides again the sugar of the
second nucleotide and the phosphate
group of the third nucleotide again the
sugar of the third new neuron and the
phosphate group of the four nucleotide
so that is how the force field
phosphodiester bond formation take place
now why is it all three - three prime
five prime phosphate is the one because
the bond formation takes place between
these two positions if you see this is
done three prime position right so it
bond formation takes place between the
three prime position and the five prime
position so here this is the
in position right and this is where the
bond formation is taking place so
basically this is where the
phosphodiester bond respond again here
if you see this is where your
phosphodiester bond formation is taking
place so the this bond is forming
between three prime and five prime
positions now whenever we talk about
these positions we refer to the position
of the carbon atom so five prime is the
carbon atom to this carbon atom they
have four straight group is attached so
we see the five prime carbon atom here
again this bond which is formed with the
sugar is through the three prime carbon
atom so the phosphodiester bond is
actually formed between three prime and
five prime positions so these
phosphodiester bonds help in joining the
multiple new blue dyes to form a poly
nucleotide so that is the significance
of phosphodiester linkage so we spoke
about three types of bonds here by
talking about the structure of a
polynucleotide one was the glycosidic
bond the second one was the forceful
Easter one and the third one is the
phosphodiester bond so let us quickly
have a look at the phosphodiester
linkage once you see here you can we can
clearly see that the nucleotides are
joined together by the phosphodiester
linkage to form a valley nucleotide now
waters Danube unite when two nucleotides
join together so this is one nucleotide
this is another nuclear right so it is
like a train with two compartments that
is a dinucleotide similarly a train with
many compartments is going to be a pony
nucleotide so here you can see this is
your dying nucleotide and this is the
phosphodiester linkage now in a very
similar way now when more and more
compartments get added to your train
so the length of the train keeps on
increasing so this is how it happens
this is sugar this is space they are
connected by glycosidic bond then sugar
and force by their link by force or
Easter bond and then phosphate and the
sugar of the next nucleotide is
connected by the phosphodiester bond so
basically this is the glycosidic bond
this is the force for Easter bond and
this one is the phospho diester bond and
in this fashion it keeps on increasing
the length of the nucleotide so this is
the structure of a polynucleotide now
whether it is DNA or RNA the structure
will remain the same so what will change
is that if it is DNA the sugar will be a
deoxyribose sugar if it is Adonai the
sugar is going to be a ribose sugar so
that is one difference the next
difference is the bases which will be
present in case of DNA and RNA so DNA is
going to have a different set of bases
there are some specific nitrogenous
bases which will be present in the
structure of DNA
similarly there are a specific set of
nitrogenous bases which will be present
in case of RNA so let us quickly have
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