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Main content
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Video transcript

so we're going to talk a little bit about DNA regulation and this is the general idea that if you look at a organism's genome that not all of the genes are being transcribed and translated at the same time it could actually depend on the type of cell that that that that DNA is inside of or it could depend on the environment for that organism so for example if you look at say a multicellular organism this may be this is in the seas these are oversimplifications right over here maybe this is some type of immune cell immune cell and let's say that this over here is a muscle cell and they're not necessarily or not likely to be these perfect circle's but this is just for the idea and they're going to have the exact same DNA so the DNA in both of these is the same so DNA is the same inside and these are going to be these are eukaryotes so I'll draw the nuclear membrane they're same DNA but they have very different roles inside of this organism so it doesn't make sense in fact in order for them to even have different structures they're gonna have to produce different proteins they're going to have different enzyme proteins inside of there inside of their cytoplasm and so DNA regulation one way to think about it is well if they have the exact same genome how do they regulate which of those genes are being transcribed and then translated and which ones aren't and even if you think about a unicellular organism right here we have a bacterium and so it's just one cell but even it will not want to transcribe and translate all of its genes at the same time for example this over here so this is its this is the bacterial chromosome this right over here might be a gene involved in the the digestion of a certain type of food if that food is present this type of and actually could even be several genes that are involved in that type of food and we will actually talk going a little bit more detail about when you have several genes that are related and they tend to be trans bribed all at once or not transcribed all at once so maybe that's related to digesting or consuming some type of food maybe you have some genes over here that are related to some type of stress mechanism maybe it needs to go into hibernation sometime and so it's not under stress it does not have to express these genes but if it is under stress it does have to express these likewise if that thing that at least a digest is around it needs to transcribe these if it's not around it does not need to transcribe it so that's where how DNA regulation works whether you're talking about a you carry out a prokaryotic organism and so what we're going to do in this video is focus a little bit more a lot more on the prokaryotes I'd especially we're going to talk about this bacterium when we talked about transcription in general and several videos ago and in several videos we talked about the idea of a promoter that you have a gene that is a sequence of DNA that's part of the broader that's part of the broader chromosome and we said okay that RNA polymerase needs to attach someplace so that RNA polymerase needs to attach someplace and we called that place that the RNA polymerase attaches we call that the promoter and then the polymerase will transcribe the gene and when we first talked about the idea of a promoter we said and this is generally true in eukaryotes that each each promoter is associated with the gene or each gene has a promoter but when we're talking about prokaryotes in this case we're talking about this bacterium it's actually typical to have multiple genes grouped together that have one promoter so the participer motor here and a promoter is actually called a a regulatory DNA sequence let me write this down so the promoter so that's this part right over here that's the sequence that is a that is a regulatory regulatory DNA sequence well that's what the RNA polymerase which I drew is this big blob it's protein here this big blob will attach to and then it will begin to transfer all of these jeans is a bundle and when you have a promoter associated with multiple genes that combination of the promoter and the genes and once again I'm talking about the promoters of the genes I'm talking about sequences of DNA that combination is called an operon this is called an operon it's a combination of that regulatory DNA sequence which says hey RNA polymerase bind here so you can start transcribing and the genes that it essentially promotes the transcription of and then of course that transcription process takes that genetic information in DNA transcribes it into messenger RNA which it can then go with the ribosomes and we have the whole translation process and this should all be review to produce the actual proteins that have functions within or even potentially outside of the cell and so we're going to dig a little bit deeper in is what can enhance this process make this happen more frequently or things that might inhibit this process in some way so as I mentioned before this is just what I had just drawn we have our big RNA polymerase blob and this is an oversimplification for what it looks like attaching to the regulatory DNA sequence which we call the promoter and then it will do the transcription which will produce mRNA which can which encodes the information in those genes but what if we're in an environment where we don't want to transcribe this particular opera this particular Siri or maybe I should say this particular series of genes well then we might something in our environment might allow repressors to take action so what are we talking about a repressor well a repressor a repressor right over here you see it you see it attaching to a sequence of DNA after the promoter and so it blocks it blocks the RNA polymerase from being able to do the transcription and so this right over here this is a protein that is called the repressor it's literally repressing the transcription and the regulatory DNA sequence where it attaches that is called the opera so once again promoter was a regulatory sequence where the where the RNA polymerase can attach and then the operator is a regulatory sequence where a repressor can attach and keep that RNA polymerase from actually being able to perform the the actual transcription and so the this keeps the gene from from keeping continuing to - to transcribe and then translate these actual genes and you might even have extra mechanisms and you can even think of them as feedback mechanisms or ways to understand the environment where the output where the repressor I should say this protein can only do its job can only so let's say that's its repressor where can only do its job if it has other molecules that attach to it so maybe this one can only do its job if it has another molecule attached to it and in that case these smaller molecules these are called co-repressors Co Co repressor repressor and we'll go into more detail when we talk about things like the trip operon of how tryptophan an amino acid can actually act as a co-repressor now over here we have the other way around where we want even more transcription in that case we would have something called we would have an activator and this let me shade it in this DNA right over here this would be the regulatory sequence where the activator binds and so this would be positive feedback when you have more activators you're gonna get more transcription while this would would be and actually I shouldn't even call it feedback because that implies that somehow these products produce the activator these products produce the repressor but that's not necessarily the case it could be you could imagine that case but it's not necessarily the case I should just say that this is repressing and this is activating it's going to make more of the transcription actually happen and just as we could have core processors small molecules that you could think of as activating the repressor you can also have small molecules that can turn the activator on and these small molecules that turn the activator on these are called inducers so this right over here these are inducers so this this protein right here couldn't activate that that operon but now that you have these inducers and we'll study that a little bit more when we think about the lac operon this could be a a small sugar of some kind well then it can turn on the activation so this right over here is called an inducer so that's just a high-level overview of DNA regulation as you can imagine this can get very very interesting and complex where you have your oppressors and co-repressors and activators and inducers that might be dependent on the environment that the cell is in what's going on and it's in its broader ecosystem there's all sorts of feedback and feed-forward loops that might be going on and that's why the study we could have the sequence and we've actually we do sequence entire genomes but even once you have the sequence it's incredibly complex to understand all of these these loops of these feedback and feed-forward loops to understand how these things actually interact with each other
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