Can transcription factors switch off genes ? - a2 biology Watch

Leah.J
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If so, how ?
I know that there could sometimes be repressor molecules bound to the promoter region which prevents the transcription factor from binding so the gene doesn't switch on, but that's the action of the repressor molecule not the transcription factor.
I also know how a TF can switch on a gene-based on what I understand, the TF binds to the promoter region and causes the RNA polymerase to bind to the promoter region starting the process of transcription.
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macpatgh-Sheldon
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Hi my young friend (!),

Transcription factors can turn genes on OR off. So answer is Yes.

Some transcription factors repress transcription. In prokaryotes, the best example is the lac repressor which blocks binding of RNA polymerase.

In eukaryotes, some transcriptional repressors compete with activators for the same DNA sequence - think of it as similar to how an enzyme inhibitor works e.g. in a similar way to how carbonic anhydrase inhibitors used as diuretics (to get rid of excess fluid from the body by increasing urine volume) compete with H2CO3 (the normal substrate) for active sites of the enzyme. Here the repressor has affinity for a particular set of nucleotides for which the activator also has affinity, yeah?

Others repressors bind to specific sites on DNA (close to binding sites of activators) and react with activators in such a way as to block their function.

Hope I have not made it too complex - ask if still struggling!
M
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humble heroics
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Perfect explanation.....here is an simulation website to demonstrate the lac operon. I use this when I teach regulation of transcription https://phet.colorado.edu/en/simulat...ine-lac-operon (does require java to run)
(Original post by macpatgh-Sheldon)
Hi my young friend (!),

Transcription factors can turn genes on OR off. So answer is Yes.

Some transcription factors repress transcription. In prokaryotes, the best example is the lac repressor which blocks binding of RNA polymerase.

In eukaryotes, some transcriptional repressors compete with activators for the same DNA sequence - think of it as similar to how an enzyme inhibitor works e.g. in a similar way to how carbonic anhydrase inhibitors used as diuretics (to get rid of excess fluid from the body by increasing urine volume) compete with H2CO3 (the normal substrate) for active sites of the enzyme. Here the repressor has affinity for a particular set of nucleotides for which the activator also has affinity, yeah?

Others repressors bind to specific sites on DNA (close to binding sites of activators) and react with activators in such a way as to block their function.

Hope I have not made it too complex - ask if still struggling!
M
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Leah.J
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(Original post by macpatgh-Sheldon)
Hi my young friend (!),

Transcription factors can turn genes on OR off. So answer is Yes.

Some transcription factors repress transcription. In prokaryotes, the best example is the lac repressor which blocks binding of RNA polymerase.

In eukaryotes, some transcriptional repressors compete with activators for the same DNA sequence - think of it as similar to how an enzyme inhibitor works e.g. in a similar way to how carbonic anhydrase inhibitors used as diuretics (to get rid of excess fluid from the body by increasing urine volume) compete with H2CO3 (the normal substrate) for active sites of the enzyme. Here the repressor has affinity for a particular set of nucleotides for which the activator also has affinity, yeah?

Others repressors bind to specific sites on DNA (close to binding sites of activators) and react with activators in such a way as to block their function.

Hope I have not made it too complex - ask if still struggling!
M
Hello friend.
Very much still struggling, let me ask this first
When I write that the TF binds to the promoter region, should I write that the TF switches some genes on and some genes off OR is the TF binding to the promoter region what activates/switches on a gene ?
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macpatgh-Sheldon
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In general terms:
1. try not to look too deep into the precise literal meanings of what you write - oc, you need to balance this with getting the right meaning and not conveying the wrong message, o-wise you lose marks.

2. my v brief advice to you would be to STICK TO SIMPLE OBVIOUS things in A level bio for max marks.

SPECIFIC TO YOUR Q:
Very much still struggling, let me ask this first

"When I write that the TF binds to the promoter region, should I write that the TF switches some genes on and some genes off OR is the TF binding to the promoter region what activates/switches on a gene ?"

Transcription factors are EITHER activators OR repressors - your first phrase implies that they can do BOTH so avoid saying that. The second phrase ("...….binding to the promoter region activates/switches on a gene") is more correct (for activators). For repressors, refer to my previous post.

M
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