RNA polymerase stops transcription at specific sites called transcription terminators. These transcription terminators are encoded by the DNA, but the signals function at the level of the RNA. Some of these processes require no accessory proteins and are referred to as row-independent transcription events. Let's take a look at this particular circumstance here. So here's our RNA molecule that we're forming.
Here's our DNA molecule. We've still got our RNA polymerase here copying our DNA molecule into RNA. So one of the structures that can form is this structure here.
This is referred to as a stem loop structure. And this stem loop structure forms by what's called intrastrand base pairing or base. bonding.
What that means is this is a single strand of RNA, just like we see up here, but we have these complementary bases that are able to form hydrogen bonds. And so that forms this secondary RNA structure that is referred to as a stem loop. Now, in addition, these stem loop structures are often followed by a series of urinodines. in the RNA.
So there would be some U's in here, and those will interact with A's, admins, in the DNA molecule. So what that means is we've got U's in our RNA molecule, and we've got A's in our DNA molecule. And the hydrogen bonds that are formed between these two bases are relatively weak.
So we get a relatively weak pairing that's occurring between the RNA and the DNA. right after this stem loop. Now, as that RNA polymerase kind of comes into contact with that stem loop and with these urinidines, what will often happen then is that stem loop will pause.
And as soon as it pauses, it causes it to dissociate, which means the RNA polymerase comes off of that DNA strand. It's actually able to go back and find another promoter and repeat this process. And also at the same time, our messenger RNA molecule is released for our next step of whatever we're going to do. We're actually going to talk about translation here afterwards. So this is row independent because all it requires is the RNA polymerase.
And there are signals here in the DNA that will allow these RNA polymerases to dissociate. While some don't require proteins, others do. So this is known as row.
dependent this is again the greek letter here for rho and what will happen in this case we've got our transcription terminator we've got our rna polymerase we've got this dna molecule here's our rna molecule but we've got a different site so we have in the dna molecule a site called the row recognition site and what that row recognition site will do is when it's copied into rna will form a site called the Rho utilization site or RUT. So this site right here is a site where the Rho protein is able to identify that particular sequence and bind to. So Rho can now bind to RUT and Rho is actually a helicase so it's going to start spinning and as it starts to spin and moves towards this RNA complex it's going to cause a separation of the DNA strand and the RNA strand. So we'll start to separate out these two strands.
And that ultimately will cause the RNA and the RNA polymerase to be released from the DNA. And again, that's going to conclude transcription in bacteria. So at the end of that process, we will have, again, an RNA polymerase. It can go back through this process.
We have our... RNA molecule, whether it's messenger RNA or transfer RNA, etc. And we have our Rho protein, which can again bind to another sequence, RUT sequence on another strand and help and assist with termination. So that concludes transcription in bacteria. As I mentioned, archaea and eukaryotic transcription is more complex.
And also there are other events that have to happen. For example, in eukaryotic RNA. molecules.
We have to remove those introns before that molecule can be moved out of the nucleus into the cytoplasm for translation.