Outlines of the major differences of the process of RNA Transcription in Prokaryotes and Eukaryotes. Major transcription stages are listen and described in detail the specific differences. The stages are Initiation of DNA transcription to RNA, elongation of the RNA strand and termination of transcription that indicates the next step of translation.
Differences between eukaryotic and prokaryotic transcription
Prokaryotic: First off, prokaryotes are simple organisms without a nucleus. Transcription and translation occurs in the same location, and therefore requires less processing of the DNA. Although both processes of transcription are similar, prokaryotic transcription is much less complicated.
Initiation: initiation of prokaryotic replication begins with at origins of replication, similarly to eukaryotic chromosomes. The region which indicates the start of transcription is called the promoter region, located near the transcribed region. To find this promoter sequence the replisome for prokaryotes RNA polymerase holoenzyme- a complex assembly of six subunits, recognize the promoter and unwind the DNA. A crucial enzyme of this complex is the sigma subunit, which positions the RNA polymerase by binging to the -10 and -35 regions and leaves after RNA synthesis begins.
Elongation: As elongation of the newly synthesized DNA occurs, a transcription bubble is maintained, where the DNA at the replication forks are unwound or rewond after transcription.
Termination: Termination is indicated by a hairpin loop structure that is formed because of complementary base pairing due to a C-G rich area and the end. This region of is called the 3’ untranslated region or 3’ UTR.
Eukaryotes have a much larger genome, with many more introns to remove therefore having a more complicated transcription process. Having a nucleus and supercoiled DNA, transcription occurs in the nucleus- newly synthesized RNA must be processed before entering translation, unlike in prokaryotic cells.
Initiation: Eukaryotic initiation requires General transcription factors or six GTFs that bind to sites on DNA to initiate transcription. The TATA box- or the site where transcription starts is bound by TFIID, or one of the six GTFs. The GTFs bind with each other and in the region of the TATA box and attracts RNA polymerase II. RNA polymerase II is a large complex of enzymes on its own has abilities that play a role in the processing of the RNA before translation occurs.
Elongation: During elongation of eukaryotic cells, many processes are occurring at once. Processing, nucleosome formation and telomere lengthening are all occurring simultaneously during the synthesis of RNA.
Organizing histones: Eukaryotic replication requires assembly and unwinding of nucleosomes, unlike in prokaryotes. Eukaryotic DNA exists as supercoiled chromatin in the nucleus. CAF-1 or chromatin assembly factor 1 brings histones to newly synthesized DNA and assembles the histones together with the help a PCNA or proliferating cell nuclear antigen. PCNA helps the CAF-1 bind to the DNA, similar to the Beta-clamp in prokaryotic transcription.
Telomere lengthening: for the risk of loosing DNA coding on the lagging 3’ end of eukaryotic DNA, the enzyme telomerase adds short repeated sequences that ensures no genetic material is lost. Although after each replication, telomeres continue to me shortened, telomerase plays an important role in maintaining the integrity of our genome.
Termination: Termination requires the processing of the RNA which includes the following. Addition of the 5’ cap and poly (A) tail on the 3’ end, as well as removal or splicing of introns.Splicing is the process of joining our exons together and removing introns via the spliceosome, or a group of small nuclear ribonucleoproteins or snRNPs. After all these processing procedures are made, the RNA is then ready to be shipped out of the nucleus and begin translation.
Griffiths , Anthony J.F., and Susan R. Wessler. Introduction to Genetic Analysis. Tenth. New York: W.H. Freeman and Company, 2010.