Course: AP®︎/College Biology > Unit 6Lesson 5: Regulation of gene expression and cell specialization
- DNA and chromatin regulation
- Regulation of transcription
- Cellular specialization (differentiation)
- Non-coding RNA (ncRNA)
- Operons and gene regulation in bacteria
- Overview: Gene regulation in bacteria
- Lac operon
- The lac operon
- Trp operon
- The trp operon
- Overview: Eukaryotic gene regulation
- Transcription factors
- Regulation of gene expression and cell specialization
The trp operon is a well-studied operon when it comes to gene regulation. It is involved in the biosynthesis of the amino acid tryptophan.
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- When tryptophan is lowered to a regular level, how does the RNA polymerase continue on with transcription? Does the co-repressor unbind itself from the repressor?(11 votes)
- The short answer is yes, when tryptophan levels are low the tryptophan unbinds from tryptophan repressor, which allows transcription of the genes.
The more more complex answer is that most chemical reactions (including tryptophan binding as co-repressor to tryptophan repressor) have an equilibrium. In biology, you are typically shown one gene, one repressor, one co-repressor. But you have to imagine the vast majority of biological processes involve 100,000 e.coli cells, each with hundreds or thousands of tryptophan repressor molecules. The more tryptophan present, the more likely it is to bind to one of those repressors and inhibit (reduce) transcription of the gene. The less tryptophan present, the less likely it will bind to the repressor.(16 votes)
- Is there a video on the attenuation of the trp operon?(4 votes)
- By Khan academy no, but i found this one.
- How does the repressor knows and come when there is too much tryptophan? (It's so intresting!) Could the repressor be functionally disordered? What happen if the repressor stops functioning?(3 votes)
- the tryptophan repressor is itself a protein produced from transcription of another gene, let's call it "repressor gene". If that gene mutated, the product of transcription of that gene (the repressor protein) could be nonfunctional. If that were the case the e.coli cell would continually transcribe Tryptophan Enzyme.(5 votes)
- what happend to the original vidoes of trp operon?(3 votes)
- Google trp operon video and click Youtube link. Good video!(2 votes)
- Why is trptophan important?(2 votes)
- Trp is one of the essential amino acids / meaning it is equally important as Methionine, Arginine or Alanine.
Its biosynthesis is vital for the rest of metabolic reactions since it is intermediate.(2 votes)
- Is gene regulation more efficient at saving energy than feedback inhibition?(2 votes)
- I'm still confused on what the co-repressor does(1 vote)
- Co repressor binds to tryptophan repressor and inhibits exšression of tryptophan repressor. You may say it actually helps gene transcription of Tryptophan.(2 votes)
- Is the trp operon post-translationally modified?(1 vote)
- Is the function of tryptophan the same in eukaryotes e.g. humans, animals, and plants or is there any difference?(1 vote)
- What if the leader sequence of trp operon gets mutated resulting in either no trp codon or a lot of trp codons in the leader sequence?(1 vote)
- [Voiceover] Two of the most studied operons are the Trp operon and the Lac operon and what I wanna do in this video is focus on the Trp operon, which is essential for the production of tryptophan, tryptophan, which you might recognize as an amino acid often associated with Thanksgiving and turkey dinner, but tryptophan, as all or most amino acids are essential for creating the polypeptides, the proteins that you use in your body and so the Trp operon, and here we're going to be talking about not your body, or we're going to be talking about something that's in your body. We're gonna talk about E. Coli. It is an operon that is on the E. Coli that is part of the E. Coli genome, and just in this diagram, the way it's drawn, it would be sitting, it would be sitting right over here. And just as a reminder, an operon is a combination of a set of genes, as well as the regulatory DNA sequences for that set of genes, in particular you have the promoter, you have the operator right over here. The promoter's where the RNA polymerase binds and would start the transcription process. The operator's where the repressor binds, and this is going to be essential for understanding how the Trp operon works. And so what are these genes actually code for? Well these genes code enzymes that are used in the construction of tryptophan, and I'm always amazed that enzymes can be used to construct what are essentially molecules that are much smaller than the enzymes themselves. In fact the enzymes involved are made up of amino acids, but then they're used to make particular amino acids, and so Trp E, D, C, B, A, they're all, once they are transcribed into mRNA and then translated into ribosomes, these enzymes are used to create tryptophan, for tryptophan biosynthesis. So let's think about how this works. So, if we are in a low tryptophan environment, our E. Coli, it needs tryptophan, it needs that amino acid as a building block for its proteins. So in that world, it makes sense that in a low tryptophan environment, the RNA polymerase can just latch on to the promoter and begin the transcription process, transcribe these five genes into mRNA which then can be translated into those enzymes and they you will have more tryptophan biosynthesis. That makes sense that you wanna create tryptophan if you're in an environment that does not have a lot of tryptophan. But what if we did have a lot of tryptophan? Well if you have a lot of something around, you shouldn't waste energy creating more of it. You have to appreciate that all organisms that are around today are the byproducts of billions of years of evolution and they've learned to be very careful, or the ones that are selected for tend to be the ones that don't waste resources, and so when you have tryptophan around, you probably don't want this transcription to occur. So it makes sense that maybe tryptophan can act as a co-repressor for a repressor molecule, for a repressor enzyme, that would attach to the operator and block the RNA polymerase from transcribing, and that's exactly what happens. So if you're in a high tryptophan environment, and tryptophan obviously does not look like these little yellow quadrilaterals over there, but that's just for our visualization purposes, and neither does RNA polymerase look like that, or neither does the Trp repressor look like that, in fact I encourage you to web search these and see how they actually look, they're fascinating. But when you have a lot of tryptophan, the tryptophan can act as a co-repressor, it can bind to the Trp repressor essentially activate it so that it'll change its confirmation so that it can then attach to the operator in the operon, and once it's attached to the operator, well then the RNA polymerase can no longer move forward with transcription. So as you can see this is a very valuable feedback loop, or not even necessarily feedback, if you're in an environment with a lot of tryptophan, don't create tryptophan, or if you just have a lot of tryptophan laying around, don't create more tryptophan. If you don't have tryptophan around, well then the repressor won't be co-repressed, I guess you can say, and then the tryptophan will actually be created. Now, tryptophan's an interesting thing because the control of transcription isn't the only place where you have some type of a feedback loop or kind of a conditional situation. You can actually have direct feedback inhibition between the proteins, and so this part isn't related to the transcription, but if this is a precursor of tryptophan, it's all very abstract in this diagram, and let's say Enzyme 1 turns into Precursor 2, Enzyme 2 turns into Precursor 3, and Enzyme 3 turns in into tryptophan, well you actually have direct feedback inhibition where tryptophan can then bind or interact with Enzyme 1 here, could interact with Enzyme 1, let me do it in a color you can see. Could interact with Enzyme 1 so that it can no longer act as efficiently taking Precursor 1 to Precursor 2. So this right over here, this is the classic feedback inhibition, feedback inhibition. The focus of this video, we're talking about operons and gene regulation, but it's important to realize that the regulation of the creation of tryptophan doesn't only occur at the transcription level and I'm not gonna go into this video, it's a slightly more advanced topic, but there's also regulation of tryptophan biases through a process called attenuation, which doesn't affect the start of transcription, but it affects how things get completed, and it will keep tryptophan from being completely, or the entire process from going to completion. But the ones that are most typically talked about are what we just talked about here, where you have your tryptophan act as a co-repressor of the Trp repressor, and also the feedback inhibition, which once again, it's not really about gene regulation, but you can see how the product of this process can go back and inhibit one of the first enzymes.