The Trp Operon - Video Tutorials & Practice Problems
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1
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The Trp Operon
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5m
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Video transcript
In this video, we're going to begin our lesson on the triptophan. And so tryptophan is an amino acid. And recall that amino acids are the monomers or the building blocks of proteins. And so tryptophan is an amino acid whose three letter code or three letter abbreviation is trp or TRP. And so tryptophan is an amino acid, and tryptophan itself can either be absorbed by the cell from the surrounding environment or taken in from the surrounding environment, or tryptophan can be synthesized from scratch by the cell. Now the trp operon is a repressible operon, which recall from our previous lesson videos means that the trip operon is usually on or active, but it can be turned off, meaning that it can be repressed, and that's why it's called a repressible operon. And so the tripeperon is a repressible operon with 5 genes, and these 5 genes are all related to each other because they encode enzymes that are required for synthesizing tryptophan from scratch. And so the trp operon is responsible for, encoding enzymes required for synthesizing tryptophan from scratch. Now, if we take a look at our image down below, notice that we're showing you an image of the TRP operon, which has these five genes, TRP, e, d, c, b, and a. And, these five genes are important for encoding enzymes for synthesizing tryptophan from scratch. And so, of course, the trp operon has a TRP operator where the regulatory protein will bind, and it also has a TRP promoter as well where the RNA polymerase will bind. Now, taking a look over on the left hand side, notice that there is a TRP regulatory gene, which is TRP r. And so TRP r is the regulatory gene that is going to encode the TRP repressor protein. And the Trp repressor protein is going to be a repressor, and so that means that it will bind to the operator and inactivate transcription. It will repress transcription. However, the TRP repressor protein is actually expressed in the inactive form, which means that when it is initially expressed, it is inactive and it will not bind to the operator. The inactive TRP r repressor protein requires a corepressor in order for it to become active and bind to the operator to repress transcription. And so the corepressor for the inactive trp r is usually going to be tryptophan itself. And so, when tryptophan, this corepressor, is bound to the inactive TRP r, it activates TRP r, and allows TRP r to bind to the operator. And when it's bound to the operator, it can repress transcription. And so if we take a look at our image down below, we can get a better understanding of this here. And so the tripperon, again, contains 5 genes required for synthesizing tryptophan, for tryptophan synthesis, and it is regulated by the TRP repressor. And so over here we have our TRP regulatory gene where you can see the TRP repressor gene, the, TRP r gene, and it has its own promoter here. So it will be transcribed and translated into the repressor protein. However, when the TRP r is expressed, it's expressed in the inactive form. And so notice we have the inactive Prp repressor, and the inactive Prp repressor on its own, it cannot bind to the operator. 1st, the inactive trip repressor needs to be bound by a co repressor. And the co repressor is usually tryptophan itself, so tryptophan can bind to the inactive trippressor to form an active trippressor. And the active trippressor with tryptophan bound can bind to the operator and repress and block transcription of the tripperon genes. And so basically, what we're seeing here is that, the trp operon, is going to be repressed in the presence of tryptophan. When tryptophan is available and present, it can serve as a corepressor to activate the trippressor, and that will block transcription. And so this here concludes our brief introduction to the trp operon. But as we move forward in our course, we're going to take a closer look at the trp operon in the presence and in the absence of tryptophan itself. And so I'll see you all in our next video.
2
concept
In the Presence of Tryptophan
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3m
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Video transcript
In this video, we're going to talk about the tripperons specifically in the presence of tryptophan. And so when tryptophan, this amino acid, is really really abundant and prevalent and found in high levels in the environment, then the cell does not really have a need to synthesize its own tryptophan. And so the tripperon, which has genes for synthesizing its own tryptophan, it's going to be inactive when there is plenty of tryptophan that is abundant in the environment. And so what happens is tryptophan is going to act as a co repressor to the repressor protein. And so the co repressor, tryptophan, is going to bind to and activate the TRT repressor protein. And so if we take a look at our image down below, we can see that cellular tryptophan is going to corepress the trp operon when it's readily abundant for the cell. And so we're specifically looking at the trp operon in the presence of tryptophan. And so when tryptophan is really really abundant and prevalent, then the cell has no need to synthesize its own tryptophan and so it needs to shut down the TRP operon. And so this is how it works. The TRP regulatory gene, which encodes TRP r, which is our suppressor protein, which has its own promoter, it's going to be transcribed and translated into an inactive TRP repressor. And the inactive TRT repressor is only going to be activated in the presence of tryptophan. And so when tryptophan is really, really, really abundant, then there's going to be tryptophan available to bind to the inactive tryptophan is going to act as the co repressor here. So the tryptophan is acting as the co repressor. And so the tryptophan co r repressor, and, that is going to form an active TRP repressor. And notice the active TRP repressor is capable of binding to the TRP operator, and when it's bound to the TRP operator, it's going to block and inhibit transcription, turning off the TRP operon. And so it's going to prevent the RNA polymerase from binding to the promoter and proceeding with transcription. And so, basically, what we're seeing here is, again, when the TRP operon is in the presence of tryptophan, when tryptophan is readily available, then the cell has no need to create its own tryptophan, And so it's going to shut down the trp operon through this mechanism where tryptophan acts as a corepressor. And so this here concludes our brief introduction to what happens to the tripeperon in the presence of tryptophan. And so moving forward, we'll be able to talk about the tripeperon in the absence of tryptophan. So I'll see you all in that video.
3
concept
In the Absence of Tryptophan
Video duration:
3m
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Video transcript
In this video, we're going to continue to talk about the trp operon, but specifically in the absence of tryptophan. And so in the absence of tryptophan, when tryptophan levels are really, really low and tryptophan is not readily available in the environment for the cell to absorb, then the cell must be able to synthesize or build its own tryptophan. And so, of course, the cell is going to synthesize its own tryptophan by using the enzymes from the trp operon. And so in the absence of tryptophan, when tryptophan levels are really, really low and tryptophan is not readily available in the environment, then the trp operon is going to be active and turned on so that the cell can make its own tryptophan. And so when cellular tryptophan levels are really, really, really low, what happens is the Trp r repressor protein is going to remain inactive. And the reason that TRP r remains inactive is because it's not going to have tryptophan, because the tryptophan is really really low, to serve as a co repressor. And so if tryptophan cannot serve as a co repressor because its levels are really really low, then trip r is going to remain in its inactive state. That means that it will not be able to bind to the operator and block transcription. And so if if it's not able to block transcription, that is going to allow for transcription to proceed and that's going to turn on the trip operon and allow the cell to synthesize synthesize its own tryptophan. And so let's take a look at this image down below to get a better understanding of how low cellular tryptophan levels results in increased transcription of the trp operon. And so we're focusing specifically on the trp operon in the absence of tryptophan when no tryptophan is available. And so notice that in this image, again, we've got our TRP operon over here on the right, and over here we have our TRP regulatory gene, which encodes for TRP r, this repressor protein. It has its own promoter. And of course, the TRP r is going to be transcribed and translated, but when it's originally transcribed and translated, it's going to form the inactive trip repressor. And the inactive trip repressor is not capable of binding to the trip operator without the co repressor, which is tryptophan itself. But if tryptophan is absent, then there's no corepressor to bind to the tripprepressor. And so that means that the TRP repressor is going to remain inactive. And because it remains inactive, this allows for RNA polymerase to bind to the TRP promoter and initiate transcription, transcribing these genes here into the messenger RNA, and then the messenger RNA will be translated into the proteins. And, again, these proteins, these enzymes, are going to help create tryptophan. And so the cell will be able to make its own tryptophan when tryptophan is absent from the environment. And so this here concludes our brief introduction to what happens to the trp operon in the absence of tryptophan, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our course. So I'll see you all in our next video.
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Problem
Problem
The trp operon consists of ________ genes that encode tryptophan biosynthesis enzymes.
A
One.
B
Two.
C
Three.
D
Four.
E
Five.
5
Problem
Problem
Under what conditions does the trp repressor block transcription of the trp operon?
A
When the repressor binds to the inducer.
B
When the repressor binds to tryptophan.
C
When the repressor is not bound to tryptophan.
D
When the repressor is not bound to the operator.
6
Problem
Problem
If the trp regulatory gene mutates so that the repressor protein can no longer bind to tryptophan what will be the result?
A
The trp operon will not be expressed.
B
The trp operon will be continuously expressed.
C
The trp operon will be expressed in the presence of tryptophan only.
D
The trp operon will be expressed in the absence of tryptophan only.
E
There will be no effect on the trp operon.
7
Problem
Problem
In the absence of tryptophan, ______:
A
The inducer cannot bind to the operator, so trp operon transcription occurs.
B
The active repressor cannot bind to the operator, so trp operon transcription is reduced.
C
The inactive repressor cannot bind to the operator, so trp operon transcription occurs.
D
The repressor binds to the corepressor, and trp operon transcription occurs.
E
The active repressor binds to the operator, so trp operon transcription is repressed.
8
Problem
Problem
Based on the information you know about the trp operon, is the creation of tryptophan expensive to the cell?
A
Yes, this is why tryptophan is the co-repressor of the trp operon.
B
No, this is why tryptophan is the inducer of the trp operon.
C
Yes, this is why tryptophan is the repressor of the trp operon.