Hi in this video I'm gonna be talking about DNA libraries. So DNA libraries are collections of DNA fragments and there are two types that I want to talk about. The first is a genomic library. So this is going to be a collection of the of the genomic D. N. A. That's done in fragment form. So how you do this is you take an organism and you take it to genome. You isolate that all of the D. N. A. It has. Um and then you cut it with these special enzymes called restriction enzymes which just cut the D. N. A. And that cuts them into fragments. These fragments then go into some kind of vector. And the vector one vector that is possibility is called a yeast artificial chromosome. And this accommodates really large DNA fragments. And this is important for genomic DNA because those fragments are going to be large because you're dealing with the entire genomic DNA. So these vectors can hold up to one million base pairs. And when I say vector, what I'm just talking about if you're unfamiliar with the term is just a you know this usually circular D. N. A. That can be used to um you can insert D. N. A. And you can take D. N. A. Out. But essentially it's used to easily get DNA into bacteria. Um And so there or other organisms. So then when you have these fragments into yeast artificial chromosomes or other types of factors you can sequence them which makes it really easy to sequence. You can express them in bacteria or other organisms. So this is what you have you have an organism with some kind of D. N. A. You then extract it digest it with those restriction in times. And so now you get all these fragments and then you put them into cloning vectors. Like I said these were these um circular DNA molecules that are very easily put into other organisms like bacteria or sequence. So that's why they're used. And so in this case we're going to express and bacteria. So now we have the vector this is the bacterial D. N. A. And we can use this to for a lot of different functions. Finding new genes evaluating functions of genes et cetera Super important. Now the second one I want to talk about is the C. D. N. A. Library. So what this is. So the genomic DNA started with genomic material right? But this actually starts with M. R. N. A. So this is going to be the RNA. That's being actively made in the cell. And so pretty much you start by taking an organism and isolating the RNA of it and by isolating the RNA. You're getting the population of genes that are actively being expressed by the south. Then you turn that RNA into D. N. A. This is called reverse transcribing. And this is also super important because now you have cut out all of the all the enTR. Ons that I meant to say all the N. Tron and you can split and all the exxons are already sliced together. So you have your actual final RNA transcript that would be made into a protein. And you just take that and you turn it into D. N. A. You then put the sienna into another vector, put it into bacteria and you can sequence it to determine what genes are being expressed. And because this is only looking at the genes that are being expressed that population of RNA is going to church change over time. So if you expose the bacteria are exposed sales to certain chemical and you extracted the RNA at five minutes and extracted the RNA at 10 minutes you're going to have different see DNA libraries because different genes are going to be expressed at different times. So um and also under different conditions. So this is a really powerful techniques to look at what genes are being expressed under what conditions. So here we have we have an organism, we have our R. N. A. We then extract it we reverse transcribe it into D. N. A. Which is here in red you put this into a cloning vector and you express it in bacteria. And then you can go onto sequence or do other studies to identify by function. So really really important technique these two DNA libraries. So with that let's now move on

DNA libraries

DNA Libraries

Which of the following libraries consists of DNA that represents the mRNA in the cell?