Transcription Video Lecture - NEET

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from exam so now let us discuss the
process of transcription so the process
of transcription RNA polymerase plays
the leading role because this helps to
create the copy of RNA looking at the
sequence or reading the sequence on the
template strand of DNA so RNA polymerase
is going to play the main role in the
process of transcription so the entire
process of transcription involves three
major steps and they are initiation
elongation and termination so these are
the three steps by which the process of
transcription takes place so let us
understand the process step by step so
we'll start with initiation so let's see
what happens during initiation so RNA
polymerase binds to the promoter of
transcription unit of DNA so that is
what will actually initiate the entire
process we need RNA polymerase for
transcription so RNA polymerase has to
come in contact with the transcription
unit and that will happen through the
promoter so this is the DNA this defines
the transcription unit of DNA that is
promoter and terminated so this is the
beginning this is the ending so this
portion is going to be the transcription
unit this entire portion so now RNA
polymerase will come and it will bind to
the promoter region okay so then RNA
polymerase combines with the Sigma
factor and forms a hollow enzyme now
what is Sigma factor so Sigma factor is
a protein which is needed for initiation
of RNA synthesis
now when I say RNA polymerase binds to
promoter what is promoter it is nothing
but a region of DNA so in that region of
DNA there is a protein called a sigma
factor so the polymerase will
actually combined with this Sigma factor
and it will form a hollow enzyme
what does hollow inside hollow enzyme is
nothing but any enzyme which is a
protein trust the core enzyme the enzyme
plus co enzyme is hollow inside what is
go enzyme it is the non protein part or
non protein component which is necessary
for the functioning of the enzyme so
basically here RNA polymerase is them
had any polymerase and Sigma factor will
join together and they will form the
follow enzyme so now once all of enzyme
is formed now why does all enzyme is
formed because the contribution is Sigma
of Sigma factor is necessary for the
functioning of RNA polymerase so now
transcription initiation is more complex
than eukaryotes when compared to the
prokaryotes why because in eukaryotes
RNA polymerase doesn't directly
recognize the promoter sequences so it
is not able to read the promoter
sequences directly so the in case of
eukaryotes some separate transcription
factors are present which mediates the
binding process that means they will
inform RNA polymerase about which
portion is the promoter again they will
bind it to the promoter so they actually
act as a mediator between RNA polymerase
and the promoter region so only after
certain transcription factors are
attached to the promoter RNA polymerase
will be able to bind to it so in case of
eukaryotes in case of the eukaryotes we
have a couple of transcription factors
which act as mediator for the binding of
RNA polymerase to the promoter region
but otherwise in the process of
initiation basically what happens is RNA
polymerase binding to the promoter
region of DNA but how will it bind to
the promoter region there are some
factors known as Sigma factors which are
essential for the functioning of the
enzyme RNA polymerase so either the
polymerase will combine with the Sigma
factor and it will form a hollow enzyme
so this is how the process of initiation
will start now another important thing
to be noted here is whenever I it is
asked where is the transcription unit of
a DNA so the transcription unit will
always be defined by the promoter and
the Terminator so now on the moment if
if I exchange the promoter and the
Terminator location for example if the
promoter is shifted this side and if the
Terminator is shifted this side what
will happen it can even change the
coding strand and the template strand
because the promoter and the Terminator
together defines which who will act as
the promoters as the template strand
which will act as the coding strand
because whether location changes
everything changes for example let me
give you an example let us suppose this
is one strand this is mother strand so
this strand is running from 3 prime to 5
prime this strand is running from 5
prime to 3 3 prime let us suppose this
is where the promoter is located right
now as we all know the promoter always
loci is located towards the 5 prime end
of the coding strand so if this is the
location of the promoter that means that
this is the coding strand and this is
going to be the template strand right so
it is the location of the promoter which
defines which one will be the coding
strand and which one will be the
template strand similarly let us
consider another scenario where you have
two strands running from 3 prime to 5
Prime and 5 prime to 3 prime and in this
case you have a promoter which is
located here so how will you know which
one is the template and which one is the
coating so promoter will always be
located towards 5 prime of coding
strands so in this case
this will become the coding strand and
this one will become the template strand
so basically the position of the
promoter and terminator decides which
strand will be coding strand and which
strand will be template strand so their
position is extremely important and also
the position of the promoter will only
define where the RNA polymerase will
come and bind to the transcription unit
so from the promoter region only the RNA
polymerase will start reading the
structural genes and finally it will end
at the terminator region so let us look
at the next step that is elongation what
happens after the RNA polymerase has
binded to the promoter region so now RNA
polymerase will facilitate the opening
of the helots so here also right now the
DNA is like the tightly bound to
double-stranded structure but we need
one strand of DNA to act as the template
strand for synthesizing RNA so for that
purpose we need to unwind the few
strands of DNA right so how it will be
how it will happen so here you can see
this was the double-stranded DNA now
this is the region where the RNA
polymerase binds to the DNA now as the
RNA polymerase moves further what it
does it keeps on opening the two strands
of DNA so you see that coiling is gone
so the two strands of DNA has been
separated in the transcription unit so
this basically bnotes the transcription
unit no once the RNA polymerase reaches
the terminated region what will happen
again this two strands which were
earlier separated by the enzyme which
agiels again start winding up with each
other to form back the double helix
structure she can see that RNA
polymerase traverses the template strand
so black one is the template strand and
pink is the coding strength now as the
ironing polymerase moves across the
template strand so it moves in which
direction it traverses from three prime
to five prime
so let us suppose this is three prime
and this is five prime and this is our
template strand so along the direction
of the template strand RNA polymerase
will move so the transcription will
happen in which direction they'll call
it will read the polymerase enzyme will
actually read the sequence of bases and
corresponding to that it will create the
complementary bases and this Tran which
will get produced will be the RNA strand
and this strand will be synthesized in
five prime to three prime direction
because both has to be anti parallel so
since this is three prime to five prime
so this one which will get generated
would be five prime to three prime so
copy of RNA is created using
complementary base pairing so that means
we're variable you have you see
different colors right that is for let
us say a TCG if you have it like this so
here also you will have the
corresponding sequence like maybe you
will have it like this say you see a G
you see a and so on so similarly you
will have it now it has been it will be
observed that finally this mRNA strand
which gets created by this RNA
polymerase is exactly identical to this
coding strand except that the timing is
being replaced by uracil so that would
be the only difference but otherwise
this RNA strand will be exactly
identical to that of the coding strand
so elongation also involves proofreading
to replace the in correctly matched
bases now sometimes it might happen that
the RNA polymerase might encounter an
error or it might commit a mistake that
is a most papers of incorrect pairing
has been done so there is a provision to
proofread and to correct the mistake but
the DNA profiling is more efficient
I'll improve living and I describe early
because of the double-stranded structure
of DNA so this process is known as
elongation because this ionic polymer is
enzyme tries to unwind the blue strands
of DNA and it elongates this portion
where the actual transcription takes
place so that is why this process is
known as elongation so here you can see
this region you can see it starts to
unwind and again in this region it
rewinds back so here it will unwind and
as soon as it reaches the terminated
region so the back portion which was
unbounded starts getting rewinded again
so this is how transcription will take
this and this is the elongation phase
and now the last phase that is the
termination for you so what will happen
here now RNA polymerase first comes it
attaches to the promoter and initiates
so that is the initiation things then it
along its the DNA transcription unit and
then it starts working on the structural
genes so corresponding to those genes it
creates a copy of RNA which is exactly
identical to the coding strand now what
happens now as it traverses through the
this portion now RNA polymerase travels
through this portion and finally it
encounters a portion of the DNA where it
encounters with the row factor and what
does this row factor row factor is the
termination factor and how you have the
Sigma factors of Sigma factor was the
initiation factor and row fact so row
factor is the termination factor so
please remember signal Sigma factor
initiation and row factor termination
now as soon as the RNA polymerase comes
in contact with these factors it changes
the functionality of RNA polymerase
so the RNA polymerase and gets this
information that okay this is the time
to stop the process of transcription so
row factor destabilizes they interact
between them next ran and newly-formed
re me let's suppose here a slim strand
will be form as soon as this RNA
polymerase reaches the row factor what
happens Valerie Bertinelli's gets the
message that the transcription process
has to be stopped and also the
connection between the newly formed RNA
and this template strand so this is the
template strand and this would be the
newly formed RNA so the connection
between these two is lost
and as a result RNA comes out of this
portion that is it comes out of the
transcription unit so the newly formed
RNA forms of the elongation complex so
here you can see this is the newly
formed RNA so this one so this newly
formed RNA will then fall off this
elongation complex and it will be
released now where will you go now just
for your information where is this
entire process taking place now this
entire process is taking place on the
DNA where is DNA DNA is inside the
nucleus so inside the nucleus itself
duplication that is replication of DNA
takes place transcription also takes
place inside the nucleus but this RNA
which is being produced it comes out of
the elongation complex of DNA but it
still remains inside the nucleus again
after a few processes take place the
match your RNA finally moves out of the
nucleus into the cytoplasm right that is
how the entire process happens so this
is how the new trans this is how the
termination will take case so basically
the initiation and termination is all
controlled by the Sigma happen at the
grow factor
so whenever RNA polymerase needs any of
these it combines with them and it is
given a message at which there is a
change in the specificity of the enzyme
that is there is a change in the enzyme
to either initiate a process or to
terminate a process so after this after
termination the RNA polymerase enzyme
dissociates and this process of
transcription stops and what happens to
the portion of DNA that was like unwind
it that means the strands were being
separated they will get back to their
previous ankle structure thank you
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