 Now, we talk about the process of transcription. Transcription is the coding of DNA into a messenger RNA. Transcription is a long process which is supported or helped out by the enzyme called RNA polymerase. As we know polymerase is the actually addition of or making a polymer. Polymer is a long molecule. Now, we simply talk about the process of transcription, how transcription occur. As we know that there are specific sets or we can say lengths of DNA on a chromosome which codes for a specific protein, we call them genes. The RNA polymerase have actually to ultimately create a gene. It does it by starting or doing or we can say transcribing the DNA in form of a messenger RNA. How it happens? The RNA polymerase identifies a specific region on the DNA that is present before the actual structural gene. We call that region a promoter region. RNA polymerase comes and binds to the promoter region. Actually, it is a very large enzyme and it attaches to the promoter region. It covers the promoter region and impart the structural gene, some initial part of the structural gene. When RNA polymerase attaches to the promoter and promoter is we can technically called upstream the gene, the structural gene. Upstream means that it is present towards the 5 prime end of the DNA. When RNA polymerase identifies the promoter region and attaches to it, it starts unwinding the double helix. Because we know that RNA is a single stranded molecule and DNA is a double stranded molecule. So, only one of the strands of the DNA are coded by the RNA polymerase into a messenger RNA molecule. So, only one strand of DNA have to act as we can called sometimes a template strand. It act as a template, a complementary to which a messenger RNA molecule is formed. So, we call it a template strand. RNA polymerase moves on the gene and open or unwind the double helix. It act it do so by breaking down the hydrogen bonds between the two strands. As we know that the two strands of DNA are joined together by the hydrogen bonding. So, RNA polymerase break down those hydrogen bonds and open up the helix, the double helix. Now, one of the helices act as a template strand. Then RNA polymerase moves on this template strand and adds nucleotides from the surrounding fluid to make an a template RNA strand. The difference is this that only the in the place of thymine a uracil base is placed. All the other bases are same adenine, guanine and the cytosine are same, but in place of thymine it adds a uracil base. The RNA strand is exactly complementary to the DNA strand. That is if the DNA if on the DNA are base sequences G, C, A, T then on our RNA it will be against G or C that is C against A or T that is G in the place of T or U, so G, U, T, T a different one exactly complementary to the DNA strand. RNA polymerase when it moves through the gene it open up the double helix. Double helix appear as a bubble inside the double helix of DNA. We call it sometimes a transcription bubble because DNA strands are open in a way that they appear as a bubble. We call it a transcription bubble. In this diagram you can see that there is a structural gene a region which have to be coded the actual gene. Before that there is a small region which is called a promoter region which is identified by the RNA polymerase. Behind you can see the enzyme and just a model or we can say model or a cartoon diagram. The RNA polymerase which is attached to a promoter region but it is extended until the initial part of the structural gene. When it properly attaches to the promoter region then it start opening the double helix and a transcription bubble is formed. Then RNA polymerase moves on the DNA strand. It moves on the gene the helix unwinds more and it makes a complementary strand of RNA. This strand of RNA protrude out of transcription bubble. When messenger RNA start forming and it start elongating then this comes out of the transcription bubble. We look at a diagram to make it clear. Here you can see a replication bubble which is actually DNA strand opened by the RNA polymerase and you can see that in blue color a messenger RNA which is forming is coming out of that transcription bubble. At end of the gene which means that where the length of DNA ends which have to code for a protein there is a sequence of DNA itself which is called a stop sequence which is actually a signal that now this gene has ended. When the stop sequence arise usually this is a series of GC that is GC base pairs guanosine and cytosine base pairs followed by a series of AT base pairs. Due to these sequences these GC base pairs makes actually join together to make a hairpin loop like structure. Just they bind in this way to each other that they make a hair structure which looks like a hairpin. We call it a hairpin loop. When a hairpin loop rises then RNA polymerase cannot go ahead and this is separated from the DNA molecule. This is the termination of the transcription and the messenger RNA is separated. It goes out of the transcription bubble RNA polymerase is separated and the DNA start winding again just like as it is normally present. So, this end of the transcription. The transcription includes initiation attachment of the RNA polymerase to the promoter region then unwinding of the DNA double strand to make a transcription bubble by the RNA polymerase. Then addition of nucleotides making a complementary strand of RNA by the RNA polymerase by addition of nucleotides. Just there is one difference that in place of thymine always azuracil will be added. Then release of this messenger RNA molecule from the transcription bubble and then the end of the sequence that is the stop sequence comes a hairpin loop is formed and RNA polymerase is separated. This is end of the transcription.