What happens in the absence of tryptophan? a. RNA polymerase...

What happens in the absence of tryptophan?
a. RNA polymerase binds to the repressor
b. the repressor binds to the promoter
c. the repressor dissociates from the operator
d. RNA polymerase dissociates from the promoter

Key Concepts

Operon Model

The operon model describes a cluster of genes under the control of a single promoter, with regulatory sequences like the operator that enable coordinated gene expression in response to cellular needs. It is a central concept in bacterial gene regulation, where genes with related functions are transcribed together, allowing efficient control of metabolic pathways.

Repressor Protein

A repressor is a regulatory protein that binds to specific DNA sequences called operators. When bound, it prevents RNA polymerase from transcribing the downstream structural genes. In many regulatory systems, the activity of the repressor is modulated by other molecules, which influence its ability to bind to the operator.

Corepressor Mechanism

A corepressor is a small molecule that binds to a repressor protein and activates it, enabling the repressor to bind to its operator and inhibit transcription. In repressible operon systems, the presence of the corepressor signals that the end product is abundant, so gene expression for its production is turned off.

Negative Gene Regulation

Negative gene regulation refers to mechanisms that decrease or inhibit gene expression, often by preventing transcription. This process is typically mediated by repressor proteins that, when activated, bind to DNA regulatory regions to block RNA polymerase access, thus controlling the synthesis of proteins in response to environmental or cellular conditions.

Transcript

00:01 So in this question, we're dealing with the trip operon, which is the operon responsible for producing the enzymes that make triptophan in bacteria.

00:14 Triptophan is an amino acid that is essential for bacteria to obtain through their diet.

00:20 And if they don't obtain it through the diet, they can make it through this series of enzymes, trip a through trip a through trip d.

00:29 So along with all of the different enzymes or the different sections in this operon, the different genes in this operand that can make the different enzymes, you have an operator and a promoter.

00:44 Okay.

00:44 So those are all the different parts of this operon.

00:47 Now, when tryptophan is present in the diet, you do not want to make these enzymes because you have.

00:59 Triptophan so if you were to block the activity of this operon then you would want the repressor to be on okay on the on the other side if triptophan is absent you want the repressor to be off okay now if this repressor is responding to the presence of triptophan that means that when triptophan is present it binds to this repressor and the binding of tryptophan to the repressor makes it more likely to bind to the dna preventing the rna polymerase from transcribing the dna.

01:42 Whereas there's no triptophan, the repressor is off of the operon and then the rna polymerase can bind and start transcribing the set of genes.

01:53 So that is the overall process of how the triptophan operon is controlled.

01:59 Now let's look at our answer choices.

02:00 Rna polymerase binds to the repressor.

02:02 Rna polymerases don't bind to repressors...

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