Introduction to Transcription

in this video, we're going to begin our introduction to transcription and so recall from our previous lesson video. That transcription is the process that builds Arna by using the DNA within a gene as the coding template. And so this is the process of building our and a now also recall from our previous lesson videos that genes are really referring to small units of DNA that encode a product. For example, a protein and so genes in order to create a protein will need to be both transcribed and translated. And so here we're talking about the first step of the process, which is transcription being transcribed now, in order to better understand transcription. It's helpful to, uh, describe some specific sequences of DNA that mark where transcription of a gene begins and ends. And so the first ah sequence of DNA that you should note is called the promoter. And so the promoter is a small stretch of DNA sequences where transcription begins, and so the promoter is really just the site where the RNA prelim a race is going to attach, and the RNA preliminaries, um, is going to be the primary enzyme involved in transcription And so the RNA polymerase, as were mentioning down below here, is going to be an enzyme, the primary enzyme that is going to prelim arise or build Arna from scratch and turns out that RNA prelim erases do not need a primer like DNA Polymerase is due on DSO. Arna proliferates does not require primer. And again, we're going to talk a lot. Maura about RNA, polymerase and transcription as we move forward in our course here. But it's important to note that the promoter is going to be the sequence where transcription begins, because this is the site where the RNA polymerase first attach is now. The Terminator, on the other hand, is also going to be a stretch of DNA sequences. But this is where transcription is going to end. And so if we take a look at our image down below, which you'll notice is on the far left, we have a chromosome, a replicated chromosome, which we know consists of DNA and protein. But if you unravel this chromosome, which you'll find is there is DNA in here and some of these DNA, some of this DNA are going to be jeans. They encode a product like a protein. And so if we take a look at a typical gene on zoom into it, which will find is that it's going to have a green region here that we're going to be referring to? Is the promoter and the promoters again? The small stretch of DNA sequences that allows for the are Nepal Emery's to bind, and this pink structure that you see here is the RNA polymerase. This is the primary enzyme involved with transcription, and so the RNA polymerase. What it does is it will bind to the gene specifically at this promoter region. And then the RNA preliminaries will transcribe the coding sequence of this gene and then the Terminator over here at the end. It is, of course, where transcription is going to end, and collectively, the promoter, the coding sequence and the Terminator. Basically, this entire region right here is referred to as the gene. Now, sometimes there are other important sequences that surround a gene, and so it's important to be able to refer to the directionality of those sequences that might be outside of the gene. And what they use are the terms upstream of the gene and downstream of the gene now turns out that downstream of the gene is referring to DNA sequences in the same direction in the same direction as transcription. And so you can see the arrow down here. You can think of little fishies downstream, and the downstream is going to represent, uh, DNA sequences outside of the gene that air in the same direction of transcription. And in this case, because the RNA polymerase binds here, it's going to be transcribing in this direction, and so downstream is in the same direction of transcription. Now the opposite direction is going to be referred to as upstream, and so upstream is going to refer to DNA sequences and the opposite direction of transcription. And so again, the RNA polymerase is binding at the promoter and transcribes in this direction. But upstream of the gene is going to be in the opposite direction of the transcription direction. And so this year concludes our brief introduction to transcription, and as we move forward in our course, we're going to continue to learn Mawr and Maura about transcription, so I'll see you all in our next video

in this video, we're going to do an overview of the entire process of transcription. However, it's important to keep in mind that as we continue to move forward in our course, we're going to continue to break down transcription and more details. And later in our course, in a separate video, we'll talk about the individual steps of transcription and more details. And here in this video, we're just doing an overview of the entire process. And so it's important to note that the two strands of DNA in a gene are referred to as either the coding strand or the template strand. Now turns out that during transcription, uh, the RNA molecules that are being built are going to have the same exact sequence as the coding DNA strand. And the template DNA strand is just going to serve as a template for building the RNA. But ultimately, the RNA molecules gonna be carrying the message that's in the coding DNA strand. And so the only difference between the RNA sequence and the coding DNA sequence is going to be the fact that it's going to be replacing all of the tees or thigh means with use or your cells and recall. That is because Arna has your cells, whereas DNA is going tohave fi means, and we'll be able to see an example an application of this down below in our example. Now it's also important to note that during transcription, the RNA molecule itself is going to be built from its five prime end to its three prime end. And it's going to be built by pairing free our DNA nucleotides, that air floating around in the cell on a DNA template. And so we'll be able to see that down below in our image over here on this side. Now this nucleotide pairing is going to occur via Watson and Crick base pairing, which recall we already covered in our previous lesson videos, which basically says that Azour Adnan's will pair with teas or thigh means. Or, in the case of DNA base pairing with Arna A's are going to be pace pairing with use because remember that Arna use are going to replace the teas. And then, of course, we know that geez are going to base pair with sees, and so if we take a look at our image down below, we can better understand the overall overview of transcription. And so this example here wants us to determine the sequence for the template DNA strand and for the mRNA transcript, given the following coding Strand. And so when we take a look at this side of the image over here, which will notice is we have a DNA molecule and recall that DNA has two strands and each of these two strands one of them is going to be the coding strand, and the other one is going to be the template strand. Uh, in this case, the coding strand is at the top here. And the, uh, template strand is the one on the bottom. And so it wants us to determine the template DNA strand sequence along with the Marna Transcript sequence that's down below. And so what's important to note here is that when we look at the coding sequence coding strand sequence, it is G A T. C. And we know that through Watson and Crick base pairing that the GSR going to base pair was sees. And so these GS here will base pair with sees on the DNA. So we know that Cesaire going to go in these positions and the A's air going to base pair with tees in the DNA. And so we will put tease here and tease Will base pair with ace and, of course, sees base pair with jeez. And so this sequence here is the sequence of the template strand sequence. Now, of course, the process of transcription represented by this arrow is going to use the DNA to build our DNA. And the DNA, as we mentioned up above, are going to have the same sequence as the coding DNA strand with this exception right here, replacing the teas with use. And so what we can see here is that the coding sequence strand is right here at the top in our DNA is going to have the same sequence as the coding strand. So it is going to be G a. And then, of course, replacing the teas with use as we mentioned here, replacing the teas with use. And so here, instead of having a tea at this position, we're going to have a you And then, of course, the sea here is going to go right here. And so this will be the sequence of the RNA. Now it turns out that in Eukaryotic cells, the Arna that is first made is called a pre m r n a transcript because it's not fully mature. But we're going to talk more details about that later in our course. Now, over here on the right were kind of showing ume or of uh so ah, zoom out of the overall process of transcription and recall that they are in a prelim Aries enzyme, which is this big pink circle. In the background is the primary enzyme involved with transcription, and so it will bind to the promoter region on a gene and start to transcribe the gene. And so when it transcribes the gene it's going to be building the RNA in the RNA is gonna be built from its five prime into its three prime end again by pairing free RNA nucleotides, that air floating around in the self on a DNA template. And so you can see that this RNA is being built from its five prime end over here towards its three prime and over here, and the direction of the RNA polymerase is to the right, so transcription is proceeding to the right And so what you'll notice is that the DNA is going to unwind, and you could see that there is a coding strand and again, a template strand. And the RNA, of course, is going to end up taking the same exact sequence as the coding string on again. This this bottom one that's down here is going to be the template strand of DNA. Uh, now you'll notice that there is going to be a region here highlighted by this box which is represented representing an RNA DNA hybrid region. And so you can see that these free our DNA nucleotides that air floating around in the cell are going to be incorporated into this Arna molecule by the RNA polymerase enzyme. And so this here is representing the overall overview of transcription. And again, as we move forward in our course, we're going to break down this process of transcription inm or details looking at it step by step by step. But for now, this year concludes our overview of transcription, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video