0:02
The most important point is in inducible
0:06
operon it is normally an off state that
0:10
is turned on or induced when a substrate
0:13
appears. Substrates act as an inducer.
0:16
That's why it is called as inducible
0:18
operon. Whereas in repressible operon it
0:21
is normally on that is repressed or
0:24
turned off when product is abundant and
0:27
the product or the end product acts as a
0:30
corpressor. So it turns off the operon.
0:34
That is why it is called as repressible
0:36
operon. The classical example for
0:39
inducible operon is a lac operon. As you
0:42
see in lac operon in the absence of
0:44
inducer this repressor protein binds to
0:48
the operator so that this RNA polymerase
0:51
cannot progress to transcribe this
0:53
genes. So operon is off or repressor is
0:57
active. In the presence of inducer as
1:00
you see this inducer lactose turns into
1:03
alo lactose acts as an inducer that
1:06
binds to this repressor and inactivates
1:10
this repressor or repressor detaches
1:13
from the operator so that this RNA
1:15
polymerase can proceed transcribing
1:17
these genes for the metabolism of
1:19
lactose. So the presence of inducer
1:23
induced or turned on the transcription
1:26
of genes. That is why this operon is
1:28
called as inducible operon. Classical
1:31
example for repressible operon is the
1:34
trip operon or tryptophan operon. In
1:37
this operon it is generally on as you
1:40
see RNA polymerase proceeds and
1:42
transcribes the structural gene.
1:44
Repressor is inactive. So transcription
1:47
is happening in normal condition.
1:50
In the presence of corpressor when the
1:53
product becomes abundant tryptophan acts
1:56
as corpressor it binds to the repressor
1:59
and activates the repressor. Now
2:02
repressor binds to the operator and
2:04
prevents the movement of RNA polymerase
2:07
for transcribing the structural genes
2:10
actually repressing the transcription of
2:13
structural genes. That is why it is
2:16
called as repressible operon. So lac
2:20
operon in ecoli activated in the
2:22
presence of lactose which acts as an
2:24
inducer to produce enzymes for lactose
2:26
metabolism. Whereas try operon repressed
2:30
when tryptophan levels are high.
2:32
Tryptophan acts as a co-pressor. Now let
2:35
us list out the difference. Inducible
2:37
operon the transcription is inactive
2:40
until induced. That is why it is called
2:42
as inducible operon. Whereas repressible
2:44
operon transcription is active until it
2:46
is repressed by a core repressor. That
2:49
is why it is called as repressible
2:51
operon. In inducible operon the mode of
2:54
action is inducer binds to the repressor
2:57
and repressor becomes inactive and
3:00
transcription proceeds.
3:02
Whereas in repressible operon co-pressor
3:05
or the end product binds to the
3:06
repressor and repressor becomes active
3:09
and stops transcription.
3:12
Inducible operon usually involved in
3:14
catabolic pathways that is breakdown of
3:16
molecules like in the case of lac
3:18
operonis lactose metabolism whereas
3:21
repressible operon is usually involved
3:23
in anabolic pathways or synthesizing
3:26
molecules as in tryptophan pathway.
3:28
Inducible operon ensures that enzymes
3:31
are produced only when needed. In lac
3:34
operon enzymes are produced only when
3:37
substrate lactose is present. Whereas in
3:41
operon it prevents wasteful synthesis
3:44
when product are abundant. In tripoperon
3:47
if the product is abundant the
3:49
tryptophan acts as the core repressor
3:52
preventing wasteful synthesis. Hope you
3:55
are clear. Thanks for joining one minute
3:57
classroom at biology sense for you. Take
