repressible vs inducible and the lac operon

[Eri3]

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Ik there's a few threads on this already but they didn't really help me on this.

So in a repressible system- transcription (tx) id always on unless a co-repressor binds to the repressor in order to activate the repressor??

In an Inducible system- a repressor is bound to the operator so tx is always off unless an inducer binds to the repressor- in order to stop the repressor from binding to the operator ?


Is my understanding correct?

Also, what type of system is the lac operon (inducible) and the tryptophan operon(repressible) ?

 

[Xo1991]

you got it right

Tryptophan = co-repressor, binds to repressor to activate the repressor; repressor binds to operator blocking transcription

Lactose = inducer. Binds to repressor, which is located on the operator. Lactose inactivates the repressor, allowing RNA polymerase to transcribe the genes.

 

[Eri3]

you got it right

Tryptophan = co-repressor, binds to repressor to activate the repressor; repressor binds to operator blocking transcription

Lactose = inducer. Binds to repressor, which is located on the operator. Lactose inactivates the repressor, allowing RNA polymerase to transcribe the genes.

so is the this an example of a positive inducible system

 

[The3nthusiast]

Ik there's a few threads on this already but they didn't really help me on this.

So in a repressible system- transcription (tx) id always on unless a co-repressor binds to the repressor in order to activate the repressor??

In an Inducible system- a repressor is bound to the operator so tx is always off unless an inducer binds to the repressor- in order to stop the repressor from binding to the operator ?


Is my understanding correct?

Also, what type of system is the lac operon (inducible) and the tryptophan operon(repressible) ?

Think of it as the name implies. Repressible system: represses the system (transcription off) unless a co-repressor attaches resulting in transcription. So the system is repressed, unless told otherwise (co-repressor)
Inducible system: the system is induced by this substrate (transcription is on) unless a substrate attaches to it resulting in shutting off transcription. So the system is induced (turned on) unless told otherwise by an attachment of another substrate.
I hope this is correct and understandable. GL

 

[denttal]

Just to clarify...

INDUCIBLE system - means that it is normally repressed but can be induced/is inducible
- LAC operon: you only want to break down lactose when there is lactose in your system. so generally the LAC operon is repressed. When there is lactose in your system, the lactose than induces the operon by binding to the repressor. Once the lactose binds to the repressor, the LAC operon can than code for enzymes, etc. that break down lactose!

REPRESSIBLE system - normally induced (system active) but can be repressed/is repressible
- the Trp operon generally codes for the making of Trytophan, so the operon is generally induced. However, when there is Trytophan in the system, you don't need to make any more of it. Tryptophan (a co-repressor) will then bind to the repressor, activating it, so that no more Trp is made!