krnkimsung

5+ Year Member
Nov 10, 2009
118
0
91
Status
Pre-Dental
Hi everyone,

" The repressor is inactive until it combines with the corepressor allowing genes to be transcribed"

True of False? I have no idea.

Thanks,
 
Dec 10, 2009
27
0
0
Status
Pre-Dental
I think maybe true...
i had a similar question on one of the practice Achiever tests..
They asked me:

Choose the Correct statements on gene regulation via a repressible system.
I. A repressor is active until it binds to a co-repressor
II. A repressor is inactive until it binds to a co-repressor
III. Transcription resumes in the absences of co-repressor

IV. Transcription resumes in the presence of co-repressor

[II & III are correct]
Explanation:
Under a repressible system, the associated proteins (end products) are usually produced continuously until the amount of such proteins formed exceeds a desired (threshold) limit. Acting as co-repressors now, the end products accumulated will begin binding to the repressors to jointly stop the ongoing transcription.


It didn't make sense to me. lol
 
Jun 14, 2009
800
3
0
Status
Pre-Dental
False? An activated repressor would halt gene transcription, not allow them to be transcribed. In repressible systems, the gene is usually on until the repressor binds a corepressor to stop it.

The other type is an inducible system, in which case the gene is usually off until the inducer binds a cofactor to start up transcription.
 
Jan 1, 2010
43
0
0
Illinois
Status
Pre-Dental
I think it is true because like the Achiever test explains: the transcription continues until the repressor binds to stop the process.
The repressor becomes active only when its other half: corepressor comes and binds to it. Then the active repressor binds to the operator and stops transcription.
repressor + corepressor = stops transcription

The corepressor is usually the end product. If too much of the end product is being made, then it joins with the repressor to stop transcription.

Hope this answer makes sense. I reviewed this material from AP cliffs bio. Maybe if you have this book, you can look in molecular genetics chapter.
 

Maygyver

10+ Year Member
5+ Year Member
Jun 14, 2008
2,309
27
91
Status
Pre-Dental
False? An activated repressor would halt gene transcription, not allow them to be transcribed. In repressible systems, the gene is usually on until the repressor binds a corepressor to stop it.

The other type is an inducible system, in which case the gene is usually off until the inducer binds a cofactor to start up transcription.
Thats what I thought at first, but if you read the question like:

"The repressor is inactive, until it combines with the corepressor, allowing genes to be transcribed"

I'm not sure if it is talking about the repressor being active or inactive. I think it might be trying to say that until the repressor binds to the corepressor, the genes are being transcribed.
 
Dec 14, 2009
423
1
0
Status
Pre-Dental
Question doesn't specify if it is repressible system or inducible system, but repressible system only used word 'co-repressor based on my memory, so if we consider it as a repressible system. it is true.

Repressible system - transcription is always on (= repressor is always inactive) -> excess of end product -> activate co-repressor -> activate repressor -> repressor inhibit transcription -> stop transcription

Inducible system - transcription is always off (=repressor is always active)

correct me if I am wrong
 

Simple Jack

7+ Year Member
Mar 15, 2010
91
2
141
Status
Dentist
yeah, this is just the simple case of negative feedback, not to be confused with the positive feedback given on this thread, not to be confused with the "beads on a string" complex of DNA+histone protein ;)
 

Maygyver

10+ Year Member
5+ Year Member
Jun 14, 2008
2,309
27
91
Status
Pre-Dental
Question doesn't specify if it is repressible system or inducible system, but repressible system only used word 'co-repressor based on my memory, so if we consider it as a repressible system. it is true.

Repressible system - transcription is always on (= repressor is always inactive) -> excess of end product -> activate co-repressor -> activate repressor -> repressor inhibit transcription -> stop transcription

Inducible system - transcription is always off (=repressor is always active)

correct me if I am wrong

I don't think that this question is asking about repressible/inducible systems.
 
Dec 14, 2009
423
1
0
Status
Pre-Dental
Maygyver I strongly advise you not to learn principle anymore, but be mature ! :)
 

Maygyver

10+ Year Member
5+ Year Member
Jun 14, 2008
2,309
27
91
Status
Pre-Dental
Maygyver I strongly advise you not to learn principle anymore, but be mature ! :)


Wow...so anytime someone disagrees with you, you get pissed? Sounds like you need to be mature. Not everyone in life is going to agree with you...doesn't mean the people that disagree with you aren't mature...Weirdo.
 
Dec 14, 2009
423
1
0
Status
Pre-Dental
Maygyver! It looks like you are the one who really got pissed !
Sorry to tell you this, but there will be no belt for you.
 
Jun 14, 2009
800
3
0
Status
Pre-Dental
Thats what I thought at first, but if you read the question like:

"The repressor is inactive, until it combines with the corepressor, allowing genes to be transcribed"

I'm not sure if it is talking about the repressor being active or inactive. I think it might be trying to say that until the repressor binds to the corepressor, the genes are being transcribed.

Agreed, proper punctuation could make the question true or false. Like how it can change the meaning of "I helped my uncle, Jack, off a horse" to... well you know.
 

Maygyver

10+ Year Member
5+ Year Member
Jun 14, 2008
2,309
27
91
Status
Pre-Dental
Agreed, proper punctuation could make the question true or false. Like how it can change the meaning of "I helped my uncle, Jack, off a horse" to... well you know.
Ha. Personally, I like this sign in bathrooms: "We aim to please, so you aim, too, please."
 

flybry2000

10+ Year Member
5+ Year Member
Oct 21, 2008
89
2
91
Status
Pre-Dental
I'm gonna beat the horse a little, I think the answer is false. In a repressible system, a repressor combines with a corepressor to halt transcription whereas an inducible system won't transcribe unless the inducer has been repressed
 

kpanesar

5+ Year Member
Dec 22, 2009
46
0
91
Status
in a repressible system, transcription is always occurring because the repressor is inactive...it needs the corepressor, which is a product of later genes, to become active so that the repressor-corepressor complex will bind to the operator and block transcription
 

TexasOMFS

5+ Year Member
Nov 20, 2009
144
2
91
Status
Dental Student
Thats what I thought at first, but if you read the question like:

"The repressor is inactive, until it combines with the corepressor, allowing genes to be transcribed"

I'm not sure if it is talking about the repressor being active or inactive. I think it might be trying to say that until the repressor binds to the corepressor, the genes are being transcribed.
That's all well and good: you can read it that way but since there are NO repressors (at least according to Genetics texts) that actually allow transcription when they are active, this way of reading it comes across as slightly nonsensical. The word repressor is self-defining: in it's active state it does not allow transcription, in it's inactive state it does.

Tutored someone on this earlier at work...Basically had to go back to the genetics book since I forgot everything about positive/negative, repressible/inducible systems. From the book's point of view, operons with repressor molecules are classified as two types of systems: negative inducible and negative repressible. Negative inducible systems are normally off and have a repressor that becomes inactive when bound to some inducer molecule. Negative repressible systems are normally on and have a repressor that becomes active when bound to some corepressor molecule. In either case, repressors in their active state, will block transcription.

The answer should be false. Omit the first comma and keep the second.