Introduction
Biology is broad and therefore embraces various topics in life that concern living organisms. Micro biology for instance deals with the study of very small organisms that are able to reproduce and sustain their generations. This is where the study of prokaryotes comes into the scene. The contrasting organisms to prokaryotes are referred to as eukaryotes. Contrary to prokaryotes, eukaryotic organisms have complex cell structures. Biology tends to full describe the complete nature of these organisms, their feeding habits, how they reproduce and where they thrive best, that is, their habitats.
Prokaryotes are single celled organisms whose cells lack the common cell components. Prokaryotic cells lack cell organelles which are mainly enclosed by a cell membrane which is common in cells that are eukaryotic. This feature of prokaryotic cells simplifies the complexity when it comes to feeding, surviving in a particular habitat or reproducing (Latchman, 2008). Contrary, eukaryotic organisms are multi-cellular organisms whose cells are complex and contain cell organelles enclosed in a cell membrane. The organelles found in eukaryotic cells have different functions that enhance the organisms’ ability to reproduce and feed. Most of the organelles in eukaryotic organisms can be defined to be specialized. This specialization is what creates efficiency when these cells want to reproduce or feed. Transcription if as well a cell activity that is quite different in prokaryotic and eukaryotic cells. The difference in how prokaryotes and eukaryotes transcript can be simply associated to their difference in cell components and structure.
Transcription can simply be defined as the replication process of the nucleic acids within the eukaryotic and prokaryotic cells. The nucleic acids in this case refer to deoxyribonucleic acids (DNA) and the ribonucleic acids (RNA). This process is aided by enzymes in the body and the process is irreversible. This gives the implication that the forward process of transcription can take place backwards. This occurs when need arises or during special circumstances when the cells want to adapt to a particular situation. The nucleic acids in the cells of both prokaryotic and eukaryotic cells contain the genetic materials that determine the characteristics of the organisms. This is the single most reason why the transcription process is very important in the lifecycle of both prokaryotic and eukaryotic cells. Due to the different nature of the cell structure and components of both prokaryotic and eukaryotic cells, the transcription process is different in prokaryotes and eukaryotes (Nicholl, 2008).
Eukaryotic transcription occurs in a series of stages: Initiation, elongation, promoter clearance and finally termination. The genetic material (DNA) in eukaryotic transcription is localized with the cell where it is later on separated from the cytoplasm to give rise to messenger RNA. Translation occurs in the cytoplasm within the cell membrane. The genetic material, deoxyribonucleic acid is also found in some cell organelles such as the mitochondria found in the cytoplasm. The DNA in the mitochondria utilizes an enzyme known as RNA polymerase in the transcription process.
The pre initiation stage in transcription in eukaryotic cells involves the presence of a core promoter sequence within the deoxyribonucleic acids which aids the transcription process. Promoters are simply locations that enable the transcription process to occur effectively. The RNA polymerase is able to bind the core promoters in a series if the essential transcription factors are available. Core promoters in eukaryotes appear in base pairs from the site of transcription (Nicholl, 2008). The most common form of a core promoter that aids transcription is the TATA box which is found in 25 – 30 base pairs up stream to the transcription site. The TATA box in this case is the binding site for the transcription process and requires the presence of the TATA binding protein (TBP). TBP is in itself a sub unit of a transcription factor referred to as Transcription Factor 2 D (TF2D). The TATA box combines with other transcription factors via the TBP to form the pre-initiation complex stage.
Promoter clearance is the stage which follows the initiation stage in eukaryotic cell transcription. This is where the promoter has to be eliminated after the bonding of the nucleic has successfully been achieved by the assistance of RNA polymerase. RNA transcripts are released and there is the probability of the formation of truncated transcripts during this time. This is one of the major similarities between eukaryotic transcription and prokaryotic transcription and is referred to as abortive initiation. Abortive initiation takes place until the rearrangement of the o factor occurs. This process results to transcription elongation complex stage. Elongation can successfully occur once the transcription successfully reaches 23 nucleotides. The promoter clearance stage is energy dependent and therefore utilizes Adenosine Triphosphate (ATP).
For elongation to occur, the promoter clearance stage has to change. In the elongation stage one DNA strand is referred to as the non coding strand is the one used as a template in the synthesis of RNA. In this case mRNA transcription can involve multiple RNA polymerase on a single strand of DNA (Latchman, 2008). This is unlike in DNA replication and hence gives the implication that multiple strands of mRNA can be reproduced from a single gene.
The termination stage is the final stage in the transcription process. This is where the multiplication of mRNA strands is stopped. This process requires energy as well and occurs in different ways in different organisms. For instance, transcription termination occurs in two different ways in bacteria. Rho independent transcription termination is one of the termination processes. RNA transcription stops when the newly synthesized RNA molecule forms a hair pin loop.
Prokaryotic transcription is not as complex as eukaryotic transcription due to the mere fact that prokaryotic cells are not as complex as eukaryotic cells. Prokaryotic transcription occurs within the cell cytoplasm and it takes place simultaneously. This is another major difference between transcription in eukaryotic and prokaryotic cells. The simultaneous process of transcription and translation in prokaryotes is impossible eukaryotes (Nicholl, 2008). This may be due to the cell specialization in eukaryotes. The genetic material in prokaryotic transcription has access to ribosome because the nucleus is not membrane bound. The stages of prokaryotic transcription are similar to the ones in eukaryotic transcription, that is: initiation, elongation and termination stages.
The initiation stage in prokaryotic transcription is characterized by a series of steps which aid in the process. A holoenzyme is formed and the process is aided by the presence of RNA polymerase. The enzymatic form is essential because it can recognize and incorporate itself into specific promoter regions. The basic promoter region in prokaryotic transcription is referred to as the Pribnow box. The holoenzyme in this stage of transcription is referred to as the closed complex. Un-wounding of the DNA structure occurs during this stage as well and the holoenzyme involved in this case is referred to as the open complex. The DNA strand in this stage is transcribed by the RNA polymerase. It however produces short non productive transcripts and they are simply regarded as abortive transcripts. Their status is so because they are unable to leave the RNA polymerase because the exit channel is blocked by the o factor.
During the elongation process, the o factor disassociates itself from the holoenzyme thereby aiding elongation. Elongation of the mRNA strands is dependent on the strength of the promoter. The strength of the promoter regions in this instance refers to the ability of the RNA polymerase and other proteins to bind onto the DNA sequence. The elongation stage requires energy in the form of adenosine tri-phosphate. The more similar the sequence between the RNA polymerase and the DNA sequence, the stronger the bond created thereby aiding elongation.
Just like transcription in the eukaryotic cells, the termination stage is the final one in prokaryotic transcription. Termination in prokaryotic transcription occurs in two mechanisms: the intrinsic termination process (rho-independent transcription termination) and the rho dependent transcription termination (Tsonis, 2003). Intrinsic termination involves a palindromic sequence that signals the RNA polymerase to stop. The sequence disassociates the RNA polymerase from the DNA strands. Rho dependent termination employs a particular factor to stop the synthesis of RNA. The factor which is used for this process is referred to as the rho factor.
Conclusion
The transcription process is one of the most important processes in living organisms specifically the eukaryotic and prokaryotic organisms. The process takes place in a completely different way in both eukaryotic and prokaryotic cells. There are a variety of similarities in both transcriptions. However the difference in the transcription process in prokaryotic and eukaryotic cells counters the similarities. Knowledge on this process is essential because it would aid in ensuring that the optimum conditions are maintained for it to occur.
Reference:
Latchman S.D. (2008). Eukaryotic Transcription Factors, New York: Rouledge.
Nicholl T.S. (2008). An Introduction to Genetic Engineering, Cambridge: Cambridge University
Press.
Tsonis A.P. (2003). Anatomy of Gene Regulation, United Kingdom: Cambridge Press.
