Before understanding the difference between prokaryotic and eukaryotic transcription, let’s first understand what transcription is. It is the process through which the genetic information in the DNA is copied to an intermediate molecule also known as RNA. In simple words, it is the process of producing RNA molecules from a DNA sequence. This transfer of information is done through the synthesis of the RNA. The RNA keeps the same information as the gene since its sequence is complementary to that of the gene transcribed.
Although the fundamental process and the chemistry behind it remain the same for both, there is a difference between transcription in eukaryotes and prokaryotes. We will compare and contrast prokaryotic and eukaryotic transcription to explain these subtle yet important differences. The Vedantu experts have summarised the differences between the two in an easy to comprehend format. But before pointing out the differences let’s look at the similarities between the two as well.
In both kinds of transcriptions, the RNA provides the template for the synthesis.
One strand of DNA duplex acts as the template in both transcriptions.
Both Prokaryotic and Eukaryotic transcriptions produce RNA molecules.
The chemical composition of both transcriptions is similar.
The enzyme RNA polymerase facilitates both kinds of transcriptions.
Now let’s look at the difference between prokaryotic transcription and eukaryotic transcription in detail.
In the case of prokaryotic transcription, both the processes of transcription and translation occur simultaneously and continuously in the cytoplasm. These processes do not occur simultaneously in eukaryotic transcription.
The transcription and translation both occur in the cytoplasm in prokaryotic transcription. However, in eukaryotic transcription, the transcription takes place in the nucleus and the translation occurs in the cytoplasm.
The prokaryotic transcription initiation is simple as the DNA is not associated with the histone protein. In eukaryotic transcription, with the DNA being associated with the protein, the process becomes complex.
The RNA processing takes place in the cytoplasm for prokaryotic transcription and in the nucleus for eukaryotic transcription.
Types of RNA
There is only one type of RNA polymerase enzyme in prokaryotic transcription and it helps to synthesise all the other types of RNA in the cells ( mRNA, tRNA, and rRNA). Eukaryotic transcription involves three types of RNA. There is RNA Polymerase I that helps in the rRNA synthesis, RNA Polymerase II for mRNA, and RNA Polymerase III that aids in the synthesis of tRNA and 5S rRNA.
RNA Polymerase Composition
RNA polymerase in prokaryotic transcription has 5 polypeptides. In eukaryotic transcription, RNA polymerase I have 14 subunits, and RNA polymerase II has 10-12 subunits.
Location of the Promoter Region
The promoter region is located upstream to the start site in both kinds of transcriptions but in eukaryotic transcription, sometimes, the promoter region is located downstream to the start site in RNA Polymerase III (present only in eukaryotic transcription).
Presence of σ Factor
One of the critical prokaryotic and eukaryotic transcription differences lies in the presence of the σ factor. Prokaryotic transcription initiation requires the presence of σ factor which is not present in eukaryotic transcription which requires initiation factors.
Binding of the RNA with the Promoter Region
In prokaryotic transcription, the RNA polymerase recognizes and binds with the promoter region with the help of the σ factor. This is possible in eukaryotic transcription only when the initiation factors are present in the promoter region.
Presence of TATA Box, CAT Box, and Pribnow Box
While the Pribnow boxes are present at 10 locations in the case of prokaryotic transcription, they are absent in eukaryotic transcription. TATA boxes and CAT boxes are not present in the promoter region in case of prokaryotic transcription and the Pribnow box is the sequence that is considered functionally equivalent to the TATA box. In eukaryotic transcription, TATA boxes are present 25-35 base pairs before the start of the transcription initiation site of a gene.
Presence of Introns
Introns are absent in prokaryotic transcription and thus there is no splicing of mRNA. As they are present in eukaryotic transcription, splicing is also present.
Modification of the Primary Transcript
An essential difference between prokaryotic and eukaryotic transcription is that the primary transcript does not undergo any post-transcriptional modification in prokaryotic transcription but it happens in the case of eukaryotic transcription.
When we differentiate between prokaryotic and eukaryotic transcription, one of the essential points to consider is the RNA capping. It is absent in prokaryotic transcription and the mRNA does not have a 5’ guanosine cap. On the other hand, eukaryotic transcription includes RNA capping that takes place at the 5’ position mRNA.
Transcription is a very important process for the Reproduction and Evolution of life on the earth. In this process the Deoxyribonucleic Acid or DNA which is a double strand polymer chain develops from the single strand polymer chain called RNA or Ribonucleic Acid. DNA is the blueprint of the life form for the organism that carries the genetic information inherited from its parents. In this process RNA is also synthesised and provides the template for the further development of DNA. During the development of organisms RNA molecules are produced from the DNA sequence.
This process may sound identical for all cases but it is significantly distinct for Transcription in eukaryotes and prokaryotes. Eukaryotes are the uniCellular organisms without any definite structure or Cell organelles. Bacteria are a good example of Eukaryotic organisms. while Prokaryotic organisms are the higher version with a well structured Cell and Cell organelles. Prokaryotic Cell organisms are widely available in the organisms of one Cell to multiCellular or complex organisms.
The main difference between Eukaryotic Transcription and Prokaryotic Transcription is that the RNA capping is absent in Prokaryotic Cells. In the Transcription in Eukaryotic Cells the capping takes place at the 5' position mRNA which is not present in the Prokaryotic Cell. In Eukaryotic Cells the cytoplasm and nucleus are the area where the RNA processing takes place in different times. While in the Prokaryotic Cells the both processing takes place simultaneously. Another major difference is the involvement of the σ factor for initiation of Transcription in Prokaryotic Cells that is absent in Eukaryotic Cells.
There are also some similarities between the Eukaryotic and Prokaryotic RNA Transcription. The chemical reaction and processes are similar in nature in both Cells and the end product is RNA molecules in both cases.
1. What is the Importance of a TATA Box in a Transcription?
A TATA box is a DNA sequence that denotes the location where a genetic sequence can be read and decoded. It sends an indication to the other molecules where the transcription is being initiated. The DNA sequence of a TATA box is commonly TATAAA. TATA boxes are located 25-35 base pairs before the transcription start site of a gene in a eukaryotic transcription but are absent in prokaryotic transcription. In prokaryotic transcription, TATA boxes are functionally substituted by the Pribnow boxes.
2. How are the Genes Different in the Case of Prokaryotic and Eukaryotic Transcription?
Prokaryotes and eukaryotes differ in transcription in that the genes are usually polycistronic in the case of prokaryotes and there are sequences for many polypeptides in a single transcript. The genes are monocistronic in eukaryotes and a single transcript code is related to a single polypeptide only.
3. What are different kinds of RNA present in a living Cell ?
The three types of RNA present in the Prokaryotic Cells are mRNA, tRNA, and rRNA. These are all synthesised from one type of RNA polymerase enzyme. However, in Eukaryotic Cells there are three types of RNA polymerase enzymes namely RNA polymerase I, RNA polymerase II, and RNA polymerase III. These three types of polymerase enzymes give rise to three types of RNA also present in Eukaryotic Cells. Along with the mRNA, tRNA, and rRNA there is also another type of RNA present in Eukaryotic Cells known as 5S rRNA.
4. Does RNA Transcription happen in bacteria ?
Bacteria are found in both types namely Eukaryotic and Prokaryotic in Cell structure. As any other living Cell RNA Transcription also occurs in the Bacterial. The two types of RNA Transcription happen in the two types of bacteria respectively. However, there is a distinct difference between the Transcription in bacteria and every other living Cell out there. Only a single type of RNA polymerase is responsible for the Transcription of all RNA Transcription that happens in the Cell of bacteria.
5. Which Book should I follow for the detailed study over the topic of RNA Transcription ?
RNA Transcription is a fundamental function of the Cell function and genetics taught in class 11 of science stream. According to the curriculum provided by the Central Board of Secondary Education (CBSE) and Indian Council of Secondary Education (ICSE) , the questions asked in the board exams at year end require students to follow the standard Textbooks. NCERT Book for Class 11 is an exCellent book for this purpose. But students aiming to get success in medical entrance exams after class 12 can refer to some other publications and guides available in the market.
6. Do I need to study the whole chapter before studying the RNA Transcription in Eukaryotic and Prokaryotic Cells ?
This topic under the chapter of Cell function and regeneration is somewhat complex in nature. Students need to be very clear about the basic structure of the Cell and the function of all the Cell organelles present in a living Cell. The basic knowledge about the RNA and DNA is very important before reading about the Transcription process performed by them. So it is advisable to learn the whole chapter in the Biology book before knowing about the topic of RNA Transcription.
7. Where can I find practice questions set for Class 11 Biology ?
The subject of biology in class 11 is all encompassing. Students get introduced to all the parts and processes in all life forms on the planet in a very detailed manner. Mere reading of the subject matter is not sufficient for the students to fetch good marks in their term exams and also the competitive exams for medical colleges. So it is better to practice the skill of writing answers for the probable questions after you finish any topic. Vedantu provides both subjective and objective questions for students preparing for the exams by themselves.