Lac Operon Function - Molecular Basis of Inheritance, Biology, Class 12 Video Lecture

hello friends this video on molecular
basis of inheritance part 33 is brought
to you by exam feel calm no more fear
from exam these bats so now let us look
at the function of the lac operon now
let us start from the beginning this is
the promoter this is the operator and
this region is a structural gene so as I
said the regulatory gene will be
functional all the time so the
regulatory gene will get expressed
continuously that means the regulatory
gene that is a gene is always active so
it is always synthesizing repressor so
they replace it which is responsible the
specific repressor for Lac operon is
being synthesized all the time so the
replacers are available all the time now
what will happen this repressor will
bind to the operator region of lac
operon
so this is the operator region the blue
region and the repression will come and
it will fit with the operator region of
the lac operon now as soon as the
repressor binds to the operator what
will happen now when the RNA polymerase
comes and tries to bind with the
promoter because that is what it has to
do it has to bind with the promoter to
start its job of transcription now when
the RNA polymerase tries to bind to the
promoter it is prevented by this
repressor that's because due to its
presence the promoter is made
inaccessible to the RNA polymerase so as
a result the RNA polymerase is not able
to continue with its job of
transcription so now what happens the
process of transcription stops that as
it is inhibited and as a result these
genes are turned off the genes lac z
lack a Lac why they are altered off so
all those enzymes which are responsible
for fermentation of
Actos they'll not be produced now do you
think that we needed all those enzymes
all the time no right
we need those enzymes only when lactose
need to be fermented but right now there
is no lactose inside the cell so we
really do not need the enzymes to
ferment the lactose so it is perfectly
fine even if these genes are turned off
right now so that means this serves the
purpose of controlling the expression of
these genes so right now all these genes
are turned off now as long as the
repressor will remain bound binded to
this operator region these genes will
remain turned off as soon as the
repressor comes out of the operator
region then the RNA polymerase will be
able to perform its job and then those
enzymes will start getting synthesized
clear okay so now let us see what
happens now as we know every organism
needs energy now every organism will
have different sources of energy so the
preferred source of energy if you talk
about in case of e.coli will obviously
be a monosaccharides like glucose where
there is no complication of breaking it
down further because it is the simplest
form of a carbohydrate so obviously
glucose would be the preferred source
but in case glucose is not available in
that case also it will need energy so
how do we provide that energy
so in that case lactose can be provided
to the growth medium of E coli
now when lactose is provided to the
growth medium of E coli what do we want
we want lactose to enter inside the cell
of E coli so how will a close enter so
for this situation the enzyme permeates
which we were talking about right so
that permeance enzyme increases the
permeability of the cell for entry of
lactose and that is how transport of
lactose into the cell take place now you
won't say that when these genes are
turned off that means none of these
enzymes
in this age whether it is funny is or it
is transacetylase or it is galactose
ideas so how from where is this bunny is
coming in now little bit of very little
amount of these enzymes remain there
because it is not necessary that when
the genes are turned off it is
completely awesome thanks they are
clicked on all very minutely so very
small amount of these enzymes might be
produced or might be present inside the
cell so with that small amount of
permeate the permeability of the cell
can be increased enough to fetch in more
lactose inside the cell
now what happens so punny is were
helping transporting lactose into the
cell so now you will start getting
lactose inside the cell
now once lactose start coming into the
cell what is the need the bacteria are
equal I needs to utilize energy so for
that lactose need to be fermented so you
will need the enzymes which are
responsible for fermentation of lactose
so let's see what happens next so now
what happens now lactose start ends
entering inside the cell so inside the
cell we have now lactose molecule so
here these purple colored molecules they
represent the lactose molecules now
lactose initiates the turn on of the
genes the presence of these lactose
molecules initiate the turn on for the
genes and that is why in the back over
on lactose this turn as the inducer
because it induces the initiation or it
induces the turning on of the genes so
let us see how does it induces the any
MN turning on of genes select those acts
as the inducer so something which
induces something so we will see that so
what happens one of these lactose
molecule will bind to the repressor so
the repressor which was bound to the
operation so one of the lactose
molecules will bind to the repressor and
as soon as the
those molecule binds to the repressor
there is some structure and changes in
the repressor as a result of which the
repressor is inactivated so the
repressor comes out the bonding between
the repressor and the operator braids
and the repressor come out of the
operator now as soon as the repressor
comes out what happens the path is all
clear for RNA polymerase so I the
polymerase will quickly bind to the
promoter and then it will continue with
the process of transcription now as soon
as it continues with the process of
transcription what will happen a strand
of mRNA will be synthesized and this
mRNA in turn will help in the synthesis
of the proteins and the proteins are
nothing but the enzymes enzymes which we
spoke about gallant societies fermions
and trans asset ideas so all these
enzymes will then be produced right so
now what happens the genes are turned on
so what what exactly initiated the
turning on of the genes the lactose
molecule and that is why lactose access
inducer now what is going to happen as
soon as you start getting these enzymes
these enzymes will start performing
their job right now once the synthesis
of enzymes had happened these enzyme
substitutes they will start doing their
job and what is their job the job of
galactose IDs is to ferment lactose that
means it will start taking nap toes and
break it down into glucose and galactose
so that means galactose IDs we actually
start reducing the number of lactose
which is present inside the cell so
gradually what will happen again the
lactose molecules will start
disappearing because beta galactosidase
will hydrolyze lactose into glucose and
galactose
now once the lactose molecules are all
gone again this repressor will bind to
the operator and again as the repressor
binds to the operator what will happen
the function of RNA polymerase will
again be blocked and therefore the
transcription will stop
so therefore every time
lactose is present whenever lactose is
present the genes will be turned on so
under what scenario genes are on genes
are on when lactose is present and that
is why lactose is an inducer and not
inhibitor right and also when the
repressor is attached to the repressor
is attached to operator
I'm sorry depression is not attached to
operator right this is the scenario when
the genes will be turned on and then
what scenario the genes will be off when
lactose is absent and whenever lactose
is absent what will happen the repressor
will be attached to the operator so this
is how the genes are being controlled
this is how the expression of genes
whether these genes will get expressed
or not whether the synthesis of protein
will take place or not that is all
dependent on the repressor and also on
the inducer
so this is how gene expression is
regulated so this was just one example
of lac operon which takes place in
e.coli there are other operons
also for example there is a trip a motor
on which acts where tryptophan plays an
important role similarly there is none
or Oberon called eval opener on so there
are several Oberon's which are
functioning in that u coli but here we
have just discussed one over on just to
give you an idea about how it takes
place so looking at this function you
can now see that this is an absolute
example of negative regulation
so whenever the repression attaches to
the operator it has a negative impact
that is the process of transcription is
stopped that is the genes are turned off
so that is why the repressor is and
repressor and it is going to cut thank
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