Structure of Operon Video Lecture | Biology Class 12 - NEET

I'm going to talk about how operons
control transcription and bacterial
cells in the next few videos in this
video I'm just going to kind of do a
basic anatomy or the operon structure of
a typical operon that you see in a
bacterial cell so what an operon
structure actually is is that it's like
a significant difference between
bacterial and ukata eukaryotic gene
control lies in the organization of
functionally related genes so many
bacterial genes have that have related
functions are clustered and under the
control of a single promoter so if this
is our promoter right here and green and
then we have these three genes right
here one two three that are all under
control of this single promoter so these
genes are often transcribed together
into a single mRNA and then a group of
bacterial structural genes that are
transcribed together along with their
promoter and any any additional
sequences that control the transcription
is called this operon so the operon
regulates the expression of structural
genes by controlling the transcription
which in bacteria is usually the most
important level of gene regulation so
right here I've drawn a basic operon
structure so right here we have the
promoter and then you'd actually have a
little bit of overlap between the
promoter so let's just draw right here
if we have in green a little bit of
overlap between the promoter and what's
called the operator right here so right
there is the operator so I'll explain
what the operator is in a second but
I'll label it for you here operator and
then here you have your structural gene
so gene 1 2 & 3 which get transcribed
into these mRNA so this is mRNA here and
then each one of these gets translated
into a separate enzyme and then each one
of these enzymes so if this is a
biochemical pathway down here the
products of the MRNA catalyze reactions
in the biochemical pathways so they are
catalyzing these intermediate reactions
between each one of these processes and
then you have your end product here and
there's a lots of different there's lots
of different products you could have
from lactose to tryptophan which are the
two most common ones which I'll explain
in further videos but that is
essentially what this operon does so you
have these genes that are transcribed
from this promoter and you have gene 1 2
& 3 which get transcribed and are
translated or it transcribed into mRNA
which then gets translated into these
enzymes which catalyze reactions without
one of these then you wouldn't have this
reaction here and your product would
stay as this little square molecule here
so you need every single one of these
enzymes to make your end product so what
if John right here is the repressor
protein so a separate regulator gene
with its own promoter encodes a
regulatory protein so it could either be
a regular regulatory or repressible or
activator enzyme so let's pretend that
this is a repressor enzyme so right here
you have your promoter right here and
then right here you have your regulator
so this is just Wikus transcribe
you have transcription into M R na and
then this gets translated into this
protein and it has a binding site here
for DNA and then a binding site here for
some sort of molecule so what this will
do is it'll actually come in and let's
pretend that this is what's called a
repressible operator so some molecule
will bind to this section right here and
that's telling this repressor to bind to
the operator so what this does is it
stops transcription so if this thing is
bound right here like this then if we
have let's do this in pink if you have a
RNA polymerase come in to start
transcription it will not be able to
bind because this repressor enzyme will
be blocking the transcription site right
so if this this promoter or actually I
kind of drew
is wrong here this repressor enzyme
should be kind of blocking the promoter
to so it's big like that it's blocking
and then it has a little molecule down
here that is bound to it telling it to
stay there right so when this molecule
becomes less abundant in the cell it
will release and then this repressor
enzyme will be released from the
promoter in the operator and then RNA
polymerase will be able to come in and
bind and then start transcription and
make these mRNA and eventually these
enzymes for this biochemical pathway
another type is called an inducible
operon so that means that this repressor
is always bound to this promoter and
operon operator so when a molecule like
lactose is a good example of this when
lactose is created it will also create
this molecule called a low lactose and a
low lactose will bind to this repressor
and release it from the operator so will
be over here and then the promoter can
come in and make the enzyme that needs
to make so that's the basic structure of
the operon so in the next videos I'll
talk about the lactose operon and the
tryptophan operon and like the
differences between a negative positive
inducible and repressible operon