Transcription is the synthesis of RNA using a DNA template. This is the first stage of the term of genes into proteins. In transcription, messenger RNA (mRNA) intermediate is transcribed from one of the stand of the DNA molecules. The transcription concepts are very similar to the DNA replication which occurs on the ribosome in prokaryotes. In replication that the DNA acts as a template and the sequence of bases in newly synthesised nucleic acid reflects that in the template strand due to the hydrogen bonding between the bases and specificity of the enzyme concerned. Transcription in eukaryotes occurs within the nucleus under the direction of three separate forms of RNA polymerase for the mRNA to be translated, it must move out into the cytoplasm. In prokaryotes (bacteria) transcription occurs in the cytoplasm.
The process of transcription is more complex in eukaryotes than in prokaryotes. Transcription is carried out by RNA polymerase enzyme, which synthesizes RNA in a 5' to 3' direction. Prokaryotes have one RNA polymerase and eukaryotes have three RNA polymerases. Each of polymers transcribed a different class of gene. Transcription can be divided into the three main stages as initiation, elongation and termination. The initiation and regulation of the transcription are under the control of extensive nucleotide sequence found in DNA upstream from the point of initial transcription.
In eukaryotes there are three RNA polymerase, polymerase 1, which catalyzes the transcription leading to most ribosomal RNAs (rRNAs ), it is insensitive to the poison, polymerase II, which is extremely sensitive this is catalyze the transcription producing mRNAs. And polymerase 111 which catalyzes transcription yielding tRNA and a small 5s rRNA component is intermediate sensitivity. The eukaryotic RNA polymerase happens between fourteen and eight subunits and two of subunits comparable to the β and β′ subunits of RNA polymerase in prokaryotic. In dissimilar, bacterial RNA polymerase, eukaryotic RNA polymerase need the help of proteins called the basic transcription factors. For the reason that they cannot initiate transcription by themselves. Basic transcription factors carry out a number of functions, which is binding to gene promoter regions, attracting the appropriate RNA polymerase to initiation site. Most genes transcribed by RNA polymerase II contain in TATA-box. TATA-box is the DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex. It found about thirty nucleotides upstream from the point where transcription begins. The TATA-box is analogous to the pribnow sequence found associated with prokaryotic gene promoters. The TATA-box includes the sequence TATAA.
In prokaryotes there are main transcription concepts carried out. For an example the most studied RNA polymerase is that from bacterium E. coli. This was helpful to find out more about the complex eukaryotes. As same as in eukaryotes the main enzyme that carried out in prokaryotic transcription is RNA polymerase and it contains four different kind of polypeptides designated as α, β, β′ and σ which are together into a complex call holoenzyme. In prokaryotes initiation occurs when the polymerase descending along the chromosome, encounters a promoter, a sequence of DNA that is recognize the beginning of a gene. The sigma component plays a regulatory function and is involved in recognition of the point along the DNA template. it called promoter, which include two sequence elements, six base pairs , called the ten and thirty five elements, which are located ten and thirty-five base pairs at same upstream of the transcription start.DNA is double-stranded, but it is only one face serves as a template from which RNA is completed.
To begin, the polymerase gets a section with seventeen base pairs, surroundings the stage for the formation of the first phosphodiester bond. Not like the DNA, the synthesis of RNA can be initiated without the required for a primer. RNA is made to connecting together ribonucleotides in an order dictated by the DNA template strand. The essence of transcription is to use the sequence of nucleotides already on the DNA strand to dictate the sequence of RNA nucleotides that will be formed into the new RNA strand. Each nucleotide along a DNA strands has adenine, guanine, cytosine, and thymine (A, G, C, and T).and each nucleotide along a RNA strands has A, G, C, and uracil (U). In here the RNA polymerase join with a RNA nucleotide with every DNA nucleotide. Conversely, before matching the DNA sequence, all polymerase pairs with matching base pairs. G is always coupled with C, so that if the DNA sequence is GGCC, the resulting RNA sequence is CCGG. Also the A of DNA is joining with the U of RNA, and the T of DNA is couple with the A of RNA, so that if the DNA sequence is AATT, the RNA sequence is UUAA. Hence, same as like DNA replication. This shows the Watson-Crick rules of base pairing in the transcription.
In conclusion, Transcription describes as the transfer of genetic information from DNA by the synthesis of an RNA molecule copied from a DNA template. Most of the general aspects of the transcription are similar in eukaryotes than the prokaryotes. In the prokaryotes initiation involved the recognition of the promoters sequence by the sigma subunit of RNA polymerase. Unlike the eukaryotes involves the recognition of promoter sequence by the transcription factors which then engage RNA polymerase to the promoter. Also initiation of the eukaryotic translation does not required any amino acid formylmethionine.Termination in the prokaryotes occurs at termination sequences depending upon the gene termination can involve the termination proteins. In prokaryotes termination is specialized. It occurs downstream of the 3' end of the mature mRNA. And also the eukaryotic transcription is required to process to produce mature mRNA. Prokaryotes RNAs are not processed. Processing involve the addition of a 5' gap the production of the correct 3'gap end by cleavage and polyadenylation, and the remove of introns by spliceosomes. A system of genetic regulation must continue if the complete genome is not to be continuously active in transcription throughout the life of all species and all cells. Highly developed Mechanisms have involved regulating transcription of the genetic information maintaining genetic efficiently in prokaryotes and the specialised associated with differentiation in eukaryotes.
