 Now we look at the process by which DNA makes a copy of itself, but this copy is not a DNA molecule. It's an RNA molecule. This process is called transcription transcribing the information which is contained in DNA transcription initiation begins at the promoter promoter is a sequence of nucleotides. This promoter has specific functions. One of that function is that it can bind RNA polymerase. So RNA polymerase is the molecule that will of course make the RNA, but it binds specific region of DNA which has the promoter. Next to promoter are genes which will be of course, their RNA will be used to make proteins. Promoter tells specific information to the RNA polymerase. It tells the RNA polymerase where to start the transcription, where to start reading from, where to start manufacturing RNA from. It also tells RNA which DNA strand to read. As you know that DNA is a double helix. There are two strands of course in the DNA. One of them the template strand is used to make RNA and the strand which is complementary to this template strand is not used to make RNA. So we can call complementary strand a non-template strand also. So this is one of the informations that promoter provides to RNA polymerase. It also gives RNA direction where to take a start that it should start transcribing or making RNA. Part of the promotion is the initiation site where the transcription will start meaning that's the part of DNA which will get converted into messenger RNA is also part of the promoter. Here once the RNA polymerase has landed on the promoter it starts putting in the nucleotides. Now these are the RNA nucleotides not the DNA nucleotides. RNA polymerase cannot use the DNA nucleotides. RNA polymerase moves from 3 prime direction to 5 prime direction. This is the direction in which RNA polymerase is moving. As I have mentioned before all poly nucleotide synthesis whether it is DNA or RNA it only can be extended or can be made in 5 prime to 3 prime hydroxyl. Remember we have talked about 3 prime hydroxyl. But RNA polymerase is basically moving in direction 3 prime to 5 prime direction. Synthesis of RNA is in 5 prime to 3 prime direction. Here I would like to mention that no primer is needed. When we talked about DNA replication I told you DNA polymerase cannot start the replication of DNA. It needs a primer and RNA inside the cell RNA a special type of RNA polymerase makes that primer to start the DNA replication process. The RNA polymerase unwinds 20 base pairs at a time and as it is moving along it is making the RNA transcript. The transcript is anti-parallel to DNA template strand. We know exactly what that means we have talked about that in detail. Another difference between making RNA and making DNA is we have talked about this the DNA errors cannot be tolerated. If there is a change in DNA it is the genetic information the master blueprint of the cell it can it is conveyed from one generation to the next generation and that can have catastrophic results. But RNA is not a radiative molecule for at least the eukaryotic cells. There is no proof reading ability in the RNA polymerase. It makes the error rate is about 1 in 10,000 to 100,000. So this RNA polymerase makes mistakes but that's okay because RNA is short lived it is made and it is degraded fairly rapidly but it has enough time to make the proteins but it does not last very long in the cell. So once the RNA polymerase has made the RNA it encounters the termination site. The termination site is also a sequence of nucleotides that tell RNA polymerase to stop the transcription process. Here I would like to mention a difference between prokaryotes and eukaryotes. In prokaryotes the DNA is not enclosed in a nucleus. It is out there in cytoplasm in the nucleoid rigid. So as the RNA is being made the translation process also starts meaning the RNA is being simultaneously concurrently made also being converted into a protein molecule. In eukaryotes the first messenger RNA that is made is called the pre-messenger RNA and it goes to modifications. We'll talk about those modifications later but the first RNA made by eukaryotes in the nucleus is the pre-MRNA. So here there is an animation. You can see it on the screen. The RNA polymerase it binds the promoter. It separates about 20 base pairs at a time. It starts incorporating nucleotides. These nucleotides are complementary to the template strand to the nucleotides of the template strand. And this transcript is also anti-parallel. We know what that means. This process keeps continuing till the RNA polymerase it's the terminator or the site where there is information for RNA polymerase to stop the transcription process. When it RNA polymerase hits that site it disengages and the messenger RNA is released. Now this messenger RNA is ready for if it is a prokaryote it can be it gets trans start that translation process starts right away. If it's a eukaryote this pre-messenger RNA that has we just made on the screen will first go through certain processes before it can be used to make protein molecules.