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Bozeman science: Gene regulation

Mr. Andersen talks about gene regulation.

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Video transcript

hi it's mr. Andersen and welcome to biology essentials video 31 this is on gene regulation in other words how we express a gene or not how we make a protein or not and I want to start with a organism that lives in our intestine called ecoli ecoli is interesting in the it eats whatever we eat and so if I eat bacon for breakfast it has to break down the proteins and the lipids in the bacon if I have cereal it has to break down the carbohydrates if I have milk it has to break down the lactose and so what's interesting about an e coli is that it can go from an organism that has zero proteins to break down lactose to one where 50% of the weight of E coli is simply enzymes the deal with lactose and it can do it like that and so how do they do that they do that through gene regulation and so in this podcast I'm going to talk about gene regulation before I do that I want to get some terminology that I'm going to use a lot out of the way and so a regulatory gene is going to be a gene on the DNA that regulates another gene somewhere farther down a regulatory sequence will usually be found just above the gene and so what do I mean by that so if DNA looks like this the gene generally will be down here that we want to express or not a regulatory gene will be somewhere else in the DNA it secretes something called a regulatory protein which then can grab on to a regulatory sequence an example to of a regulatory sequence I'll talk about is called the promoter once this is all fit up then we can have an RNA polymerase actually make the gene and so I'll go through that terminology but when I'm talking about regulatory gene regulatory sequence those both deal with DNA but when I'm talking about a regulatory protein that's coming from somewhere else to help express the gene or not as far as gene regulation examples most of what we know now comes from bacteria and so I'll talk about positive and negative control positive control example I'll give you used the lac operon that deals with lactose and the negative control is the trip operon deals with tryptophan and then finally I'll show you what we about eukaryotic gene regulation and how they use transcription factors as activators repressors to either express a gene or not and so this is how genes are made or expressed remember we start with DNA and that DNA eventually makes messenger RNA which eventually makes proteins and those eventually make you and so any step along the way we can actually regulate the gene so we can regulate it post translationally post transcriptionally so we can do it everywhere but in general most of the regulation i'm talking about is just going to be from DNA to messenger RNA do we express the gene or do we not and so this is generally what goes on we've got a gene like this upstream of that we have a regulatory sequence an example of this in eukaryotes would be the tatah box and the reason it's called the Tata box is you have a thymine adenine thymine adenine and on the other side you'd have to add a backwards complementary to that and so this is simply a sequence above the gene that allows the RNA polymerase to get on and so we have a regulatory protein coming from somewhere else remember another regulatory gene may be downstream or upstream from this whole gene the regulatory protein an example could be the tatah binding protein this is found in us it'll grab on to the tata box let me get rid of the writing and it allows RNA polymerase to grab on and actually express that gene and so if we didn't have the sequence if we didn't have the regulatory protein we couldn't make the RNA polymerase and we couldn't make the protein and so that's basically how genes are regulated or not and so let's talk about how this works in the lac operon in bacteria because this is the first one that we really started to understand so the way they tweaked what I just said is the the neat thing about bacteria is instead of just having one gene they'll have a number of genes and so they'll have three genes all the genes required to deal with lactose will be put right next to each other and so we've named those the lac z/y and but they each make a protein and they each help break down lactose above that they'll have a regulatory sequence called a promoter remember that's going to be where RNA polymerase grabs on and the other thing they'll have in an up operon is called an operator an operator sits right between the promoter and the genes and the way I like to think about it is it's like an on-off switch and so it can either be set in an on position or it can be set in an off position and so it regulates whether or not we turn the genes on or we don't the other thing that I'm going to add here is something called the repressor a repressor will plug right into the operator so it's going to fit right here and as long as the repressor is available RNA polymerase can't get on and so this would be when the presser is here the operator is now in the off position in other words we can't make these genes this repressor I'm going to show you is is showing what's called positive control what do we mean by positive control what I said was when lactose shows up we want to make all the proteins to break down and deal with lactose and right now there's no lactose present and so it's off but let's say lactose shows up in other words I drink a glass of milk now there's lactose so the lactose shows up the lactose you'll notice is going to fit perfectly into that repressor and when it fits in the presser it changes the conformation or the shape of that protein in other words now the repressor doesn't fit in the operator anymore in other words it slacks these little prongs will say that fit in the operator okay so lactose is present repressor is now off well who can grab on RNA polymerase now fits RNA polymerase can fit there's no repressor RNA polymerase is going to run down it's going to make each of the messenger RNAs for each of those lac genes each of those are going to make a protein and each of those are going to break down the lactose and so we can deal with a lactose and we can metabolize that lactose so now the lactose is gone what's happening to our repressor it's going back to that original shade and so it's a cool way we can have positive control the lactose shows up then we make make all the proteins that can actually deal with that lactose shows up again we're gonna get rid of that repressor and we continue and so that would be positive control what's an example of negative control well a negative control we learned about from the trip operon trip operon instead of having just three it actually has five different genes but they're put right next to each other in the same way the way it works is it's actually off when tryptophan or whenever that chemical is present and so tryptophan remember is an amino acid we need it to make proteins and so bacteria as long as tryptophan is present they don't want to have to make tryptophan on their own and so the way it works here is that the actual tryptophan fits in the repressor it gives it a shape that actually blocks the RNA polymerase are the making of those proteins but let's say for example that your diet doesn't have tryptophan so you're not getting tryptophan in your diet what does the bacteria do well now the repressor is gonna change shape it's gonna change shape that allows RNA polymerase on RNA polymerase is going to quickly make those five proteins and then those five proteins are going to make more tryptophan so the tryptophan fits again and it's going to turn off and so what that gives us is really cool control as far as the bacteria goes on if we have positive control in the case of lactose whenever it shows up then we want to break it down or tryptophan control negative control when it's when it's there then we want to turn it off so simple neat engineering solution to a real-world problem now we don't have operons remember in between each of our genes we'll have long stretches where there's actually junk quote-unquote DNA and so the way it works in us is a little bit different we use what are called transcription factors so RNA polymerase is here but RNA polymerase can't get on until we have a number of transcription factors of present and so let's say we want to make a protein as well and eukaryotes to do that we have regulatory factors those are actually made by regulatory genes that could be somewhere else in the DNA or they could even be outside the nucleus and this plasm so in order for us to transcribe a gene it takes a little bit more it's a little more in-depth first of all the transcription factors will allow the attachment of RNA polymerase will have other transcription factors that will actually hold it in place but you can see that we're not actually making the gene and so in order to make the gene the DNA upstream of that will actually have to fold it'll get more transcription factors and you'll notice that still nothing's going on we still don't have transcription until that actually folds back and activates that RNA polymerase can go now and make that protein or make the RNA and then eventually make the protein and so how does it work in us we don't really have these on/off switches I don't know if you can see my hands but what happens is the DNA actually folds back on itself and it can activate genes and other places along the genome and so it's a different form of control it's more complex form of control but it really requires input from all these other transcription factors so that's gene regulation and I hope that's helpful