Difference between transcription and translation

The process of converting RNA (ribonucleic acid) from the template of DNA (deoxyribonucleic acid) is known as transcription. However, when the RNA template (mRNA) is converted into protein (sequence of amino acids), is known as translation.

We can also say that transcription is the initial step in gene expression, which gives rise to the primary transcript in the form of mRNA with the help of the enzyme RNA polymerase. While translation is the formation of the polypeptide chain, where mRNA templates bind to ribosomes and decode the mRNA template for amino acid formation, it has a segment code of 3 bases each and these amino acids together constitute a polypeptide chain known as a protein.

The above lines are the simple way to explain the process of the central dogma of life. But the actual process is tedious and is carried out with high fidelity.

We all know that every cell Earth’s living cell stores its information genetics in the form of DNA, which are double-stranded nucleic acids. They are long polymeric chains and are composed of four monomers and are named adenine, guanine, cytosine and thymine or single monomers such as A, G, C, T respectively. These monomers are linked in a linear sequence and encode genetic information.

These processes are common to all living organisms. To transfer genetic information, DNA must make more than one copy of itself, and is then expressed by the mechanism of RNA and finally protein synthesis. So, in this content, in order to highlight the difference between the two main processes (transcription and translation), we will also summarise them.

Comparative table

Definition of transcription

Just like the structure of DNA, RNA is also made up of the chain of nucleotides linked by phosphodiester bonds. But there are many differences between the two, and among them, one of the main differences is the strand, where DNA is double-stranded or has two polynucleotide strands, while RNA is single-stranded. As we know, all RNA is synthesised from the DNA strand only through the process of transcription. It is considered as the way genes are expressed.

The process of transcription is mediated by the enzyme RNA polymerase and produces messenger RNA (mRNA), tRNA and rRNA. This process occurs in both types of organisms, i.e. prokaryotes and eukaryotes, but with a slight difference.

However, in eukaryotes, the mRNA produced in transcription is translated after processing, but in prokaryotes it is translated directly. Secondly, in eukaryotes, the process of transcription and translation is separated by the nuclear envelope, i.e. transcription occurs in the nuclear envelope and translation in the cytoplasm, whereas in prokaryotes both processes occur in the cytoplasm.

Transcription does not take place in the entire DNA template, but takes place very specifically in some of the regions only. The exact reason is not yet known, but gene expression is said to take place in the required part of the DNA template. The transcription process takes place in three steps in both prokaryotes and eukaryotes: Initiation, Elongation and Termination.

Transcription in prokaryotes

Initiationto initiate the process, there is an enzyme called RNA polymerase that binds to the DNA template in the specified area known as the promoter region, which enhances or signals RNA synthesis. But because there are two strands of coding DNA, it is the job of the sigma factor (one of the subunits of RNA polymerase present in E. coli) to recognise and initiate the process.

Now, together, the RNA polymerase and other factors are called transcription initiation factors that recognise the promoter regions which are the TATA box or Pribnow box, this box consists of the six nucleotide bases (TATAAT) and the ‘-35’ sequence and has TTGACA nucleotides for recognition. These regions are located on the left-hand side and 10 and 35 bases respectively from the transcription start point.

ElongationAs soon as the promoter regions are known, the transcription process starts from the 5′ end to the 3′ end, which is antiparallel to the DNA strand. RNA polymerase unwinds the DNA double helix and proceeds along the bases 10-20 times.

TerminationTo stop the process there are two types of factors, called Rho-dependent and Rho-independent termination factors. Rho factors are the protein that provides or acts by binding to the growing RNA and, therefore, mRNA synthesis will be stopped and the DNA polymerase will also dissociate. Rho-independent factors act through the formation of a hairpin structure by the RNA and cause termination of the transcription process.

Transcription in eukaryotes

The process in eukaryotes is similar to that of prokaryotes but is more complicated, in this type there are three RNA polymerases, which is RNA polymerase I, II and III. These polymerases play different roles in the transcription process, RNA polymerase II is responsible for the synthesis of mRNA and snRNA.

Here is the sequence, which is present in the upstream region of the DNA sequence and which is almost similar to the Pribnow box in the prokaryote. This sequence is called the TATA box or Hogness box. Another sequence called CAAT box is another site that supports the initiation of transcription.

There are other molecular events necessary for initiation, which are assisted by transcription factors (TF), namely TFIID, TFIIA, TFIIA, TFIIB, TFIIF, TFIIE, TFIIH, these factors bind to promoter regions and assist in transcription. The enhancer can stimulate the process 100-fold; they work by binding to transcription factors and together they are known as activators.

Post-transcriptional modifications

The RNA produced by RNA polymerase II after the transcription process is the primary mRNA transcript in eukaryotes. These mRNAs undergo many types of modifications that are called post-transcriptional modifications. These modifications take place on both sides of the transcript and include splicing, base additions, base modifications, etc. These changes to the mRNA are made with high fidelity.

Alterations to each of the pre-mRNAs are made at the 5′ end and at the 3′ end the poly-A tail is added.

These alterations are useful to the mRNA in many ways, since they make the ribosome to recognise the 5′ end and bind, it also inhibits the action of the hydrolytic enzyme and promotes mRNA transport.

Definition of translation

Translation is the process of gene expression in the form of proteins in a living cell. In both eukaryotes and prokaryotes it occurs in the cytoplasm of the cell. Here ribosomes play the most critical role, as the mRNA leaves the nucleus and binds to this cellular machine. The reason why only mRNA is used for the process is that mRNA is messenger RNA and carries messages or genetic information from DNA to protein.

The process starts when mRNA binds to ribosomes and the ribosomes attract another RNA called tRNA (transfer RNA). This tRNA carries specific amino acids, which generates the matching mRNA code that carries the sequence of three bases.

As soon as the three-base sequences of the tRNA and mRNA match, they begin to pair with their complementary three-base sequence and the tRNA begins to deposit the amino acids and the process continues. The polypeptide chain arises when one amino acid binds to another, resulting in a final protein.

This process is not so easy, there are certain precursors that initiate the process, first, the ribosome decodes the mRNA chain, the aminoacyl tRNA or tRNA containing the specific amino acids binds to the complementary three-base sequences. This process is also completed in three steps, initiation, elongation and termination.

Initiation: ribosomes bind to the target mRNA strand. Methionine is the first tRNA added, which is paired with the AUG codon (start codon) of the mRNA. The process starts from the 5′ end of the mRNA strand. A complementary amino acid is added to the three nucleotide sequence of the mRNA; these three nucleotides are called a codon.

Elongationafter the first amino acids are paired, the tRNA moves to the second codon to pair other amino acids; in the same way, the process continues and forms the chain from the 5′ end to the 3′ end. The peptide bond is formed between the two amino acids.

TerminationThere are three termination codons or stop codons, UAG, UGA and UAA. Whenever ribosomes encounter any of these codons, they stop moving and release the polypeptide chain.

The distinction between prokaryotic and eukaryotic translation is the size of the ribosomes, as in prokaryotes the ribosome is 70, while in eukaryotes it is 80. Even prokaryotes have the Shine-Dalgarno sequence, which is the starting point of the coding sequence and this is where the ribosomes bind.

Genetic information is translated from the four letters of the polynucleotide alphabet into the 20 letters of the protein alphabet. There are 64 possible combinations of nucleotides, and these genetic codes are universal in all species, except the mitochondriawhich creates its proteins.

Post-transcriptional modification

Post-transcriptional modification is for the newly synthesised polypeptide chain, which is aimed at forming the appropriate structure by interaction with ionic bonds, hydrophobic bonds, Vander Waals, etc. and other modifications such as glycosylation, acetylation, amino-terminal modifications, carboxyl. -terminal modifications.

Key differences between transcription and translation

The following points highlight the main difference between the process of gene expression, which is transcription and translation:

1. After the replication process, the next step is transcription, where RNA is synthesised from the duplicated DNA. The next stage of gene expression is protein synthesis called translation, here the protein or polypeptide is synthesised from the mRNA.
2. Transcription occurs in the nucleus in eukaryotes and in prokaryotes, in the cytoplasm, while translation occurs in the cytoplasm in both.
3. The main role in transcription is played by polymerase, while in translation ribosomes play the essential role.
4. Transcription occurs when RNA polymerase (enzyme) acts along the DNA template strand. Post-transcriptional modifications involve cutting, splicing, folding, modification of nitrogenous bases and addition of specific end-groups. Translation, on the other hand, begins when a ribosome complex interacts with the mRNA strand. Post-transcriptional modification involves modification of the amino acid chain such as sorting, packaging, glycosylation and acetylation.
5. DNA is the template strand in transcription, while in translation the mRNA acts as the template strand.
6. Splicing is necessary in transcription, where introns are separated from the primary transcript; it is also a type of mRNA strand modification, although it is not necessary in translation.
7. Phosphodiester bonds exist between nucleotides in the RNA formed, while peptide bonds are present between amino acids in polypeptide chains in the translation process.
8. Inhibitors or antibiotics to stop the transcription process are Rifampicin, Actinomycin D and 8-Hydroxyquinoline, while Streptomycin, Chloramphenicol, Tetracycline, Cycloheximide, etc. are used to inhibit translation.

Similarities

• Both processes require a template.
• Both are the chemical mechanism.
• The nucleotides needed are adenine, guanine, cytosine and uracil.
• The process is completed in three steps: initiation, elongation and termination.

Conclusion

In this content, we discussed transcription and translation, which are considered the main steps of protein synthesis; in our previous publication we already dealt with replication. However, we can say that these studies have been useful for us not only to gain knowledge but also to know the science in depth and to be able to do more research on them. It is also useful from a medical point of view.