“The process of transcription and translation is a part of the cell central dogma system helps in tailoring an amino acid sequence from the gene.”


The replication, transcription and translation are the part of DNA metabolised in which a new DNA, mRNA and protein constructed, respectively. 

All three processes are collectively called a cell central dogma.

The transcription is an intermediate step of this process which formed an intermediate transcript whereas the translation is the final step of protein construction. 

Though both processes are allied with one another but are not similar. Actually, we can say it is not related because both occur in a different part of the cell. 

Related read: DNA story: The structure and function of DNA.

Definition of transcription and translation: 

The process of mRNA construction from a gene using the RNA polymerase is known as transcription. 

Whereas 

The process of constructing a chain of amino acid- a protein using tRNA and rRNA is known as translation. 

The occurrence of transcription and translation: 

The transcription occurs in the nucleus of the cell, once the DNA is copied through the replication, immediately the process of transcript formation started. 

The translation occurs in the cytoplasm of the cell, specifically, at the ribosome, the process of protein formation happens. 

Once the mRNA is formed in the nucleus, it migrates from the nucleus of the cell to the cytoplasm at the ribosome at where the entire process of translation leads to the construction of the polypeptide chain. 

Steps in transcription and translation: 

Both transcription and translation are broadly divided into three categories: initiation, elongation and termination. 

Transcription:

Initiation: 

During the transcription, in the initiation step, the RNA polymerase II binds to the newly formed DNA at the site called promoter, located at the beginning of a gene. 

A promoter is a unique non-coding sequence or recognition sites at which different transcription factors bind.

Elongation:

In the elongation step, the gene starts unwinding, the RNA polymerase recognises each base and accordingly starts inserting complementary base pairs. 

Termination:

The RNA polymerase completes the mRNA synthesis and detached once it reached the termination sequence.

A single-stranded mRNA is now formed from the DNA which is called a “transcript”. 

Graphical illustration of the process of transcription and translation.

Graphical illustration of the process of transcription and translation. mRNA is formed from the DNA through transcription while a chain of amino acid translated from the mRNA.

Translation:

Initiation:

During the translation, in the initiation step, the smaller and larger subunits of ribosome bind to the mRNA transcript at its binding site. 

The process of constructing protein is started when the start codon AUG is recognised by the tRNA. 

Elongation:

During the elongation phase of the translation, the mRNA triplet codon is “read” and complementary amino acid is added by the tRNA. The entire reaction is catalysed by ribosomal RNA. 

Termination:

Once the termination codon is reached, peptidyl tRNA stops the synthesis of the polypeptide chain.

(Note: there are other transcriptional factors and translational proteins are involved in both the process however we have explained the entire process in short).

Here in the transcription, the entire process is depended on the activity of the RNA polymerase whereas no polymerase is involved in the translation. 

Interesting, We can say, transcription is a process of encoding information in the form of mRNA (messenger RNA) while the translation is a process of decoding the information present in the mRNA. 

“Collectively, encoding and decoding information from the mRNA is known as gene expression.”

In the eukaryotes, the transcription and translation occur in the nucleus and cytoplasm, respectively. While in the prokaryotes the entire process occurs in the cytoplasm only. 

Antibiotic rifampicin inhibits transcription while puromycin and anisomycin inhibit translation. 

The final product of the transcription is mRNA – messenger RNA made up of the Adenine, Guanine, cytosine and Uracil. It has the starting codon at the leading site and termination codon at the end. 

The 3’ end of the mRNA is called a poly-A tail due to the presence of a long chain of adenine. 

The final product of the translation is a long chain of amino acid- a basic building block of a protein called a polypeptide chain. 

The first amino acid of the amino acid chain is the methionine. (Although it is removed in most cases). 

Read more: DNA To Protein- A Brief Overview Of Gene Expression.

The final product of transcription and translation: 

The final product of the transcription is mRNA which is directly used in the translation once it migrates to the cytoplasm. 

Whereas the final product of the translation is a chain of amino acid, although it does not directly form a protein. 

In the later stage, as per the requirement, the chain of amino acid or different chain of different amino acid folds and coiled on each other to form a different protein. 

Some proteins are made up of the single amino acids chains while some are made up of the multiple amino acid chains. 

It is also creating primary, secondary, tertiary and quarternary proteins molecules as per the requirement of cells. 

Furthermore, a protein also collaborates with other molecules for serving different functions. For example, a lipoprotein is made up of lipid and protein serves a major function in cell wall construction. 

Summary of the article: 

Transcription  Translation 
Location  Nucleus  Cytoplasm (At ribosome)
Final product  mRNA (messenger RNA) Polypeptide chain 
Property of fina product  poly-A tail at the 3’ end, single-stranded and contains starts and stop codon. Amino acid joined by the polypeptide bonds.
Components used  RNA polymerase and transcriptional factors  tRNA, rRNA and other translational factors. 
Information  Encoding information into mRNA  Decoding information from mRNA
Steps Initiation, elongation and termination Initiation, elongation and termination
Starting molecule  A polynucleotide sequence- gene  An mRNA 

Conclusion: 

Within a second transcription and translation occurs, a specialised set of genes present in our genome regulates the entire process called housekeeping genes. Those genes regulate the rate and amount of gene expression in each cell and tissues as per the requirement. 

Thus for forming a proper protein, a proper mRNA must be created first and before that, the DNA must be copied properly during the replication. 

For performing all theses function, housekeeping genes must transcribe properly. We can say its a circle in which all the steps or process is depended on others. 

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