Difference Between Introns and Exons

Introns or the intervening sequence are considered as the non-coding part of the genes, while the exons or the expressed sequence are known to be as the coding part for proteins of the genes. Introns are the common attribute found in the genes of the multicellular eukaryotes like humans, while exons are found in both prokaryotes and eukaryotes.

The traditional method for the flow of biological information in the living being is that the DNA makes RNA and then RNA makes proteins. These methods are also known by their name as Replication, Transcription, and Translation.

Starting from the replication, which is known as the process of copying of deoxyribose nucleic acid (DNA) to produce the identical copy of the DNA molecules itself. Then comes the transcription which is the synthesis of the ribonucleic acid (RNA) from the DNA. Finally, the stored genetic information is expressed in the form of proteins, this is known as translation.

Targetting the transcription where the entire DNA is copied into pre-mRNA (primary transcripts), and these sequences are made up of introns (the non-coding regions) and exons (the coding region), notably, in the eukaryotic genes.

Further, this pre-mRNA undergoes many alterations like end modifications, splicing, etc., which are collectively called as post-transcriptional modifications. Here the introns are removed, and exons are joined to form a contiguous coding sequence. This process is performed to convert pre-mRNA into its active form called as mature mRNA, which is ready for the translation.

At this moment, we will discuss in differences between the introns and exons followed by a brief explanation.

Content: Introns Vs Exons

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Definition of Introns

An intron is a nucleotide sequence present in DNA and RNA; these are the intervening or interrupting sequence found between the two exons. They range from the 10’s to 1000’s of base pairs. These are found in the eukaryotes like humans.

Introns do not code for protein directly, but they are the part of transcribed pre-mRNA (primary transcripts). Introns are needed to be removed before the mRNA converts into the proteins. So for this, the pre-mRNA undergoes the process called splicing.

Splicing or RNA splicing is one of the post-transcriptional modifications steps for the removal of introns; it is the important process which is done very precisely. This modification is supported by the small nuclear ribonucleoprotein particles (snRNPs) or snurps. These snRNPs are formed with the association of the small nuclear RNA (snRNA) with proteins. Together they are called as the spliceosome.

Splicing occurs at particular splicing sites, and they begin with the nucleotides present as GU at 5′ ends and AG at the 3′ end. The snurps binds at both the ends of the intron and forms the loop, and then the intron is removed from the sequence, and the exons are joined together. Post-transcriptional modifications occur in the nucleus, after which the mature RNA (mRNA) moves to the cytosol to perform the function of translation.

Why is introns removal essential?

As we discussed before, that introns are non-coding part of the nucleotide sequence as well as not highly conserved. So it is necessary to splice off or remove the introns to avoid the production of the wrong or incorrect protein. As if any introns got left or any exon got deleted, all the faulty proteins will be produced.

This occurs because the amino acids which make the proteins are based on the codons left over after the post-transcriptional modifications. The three nucleotides present in the sequence, make up the amino acid and proceeds with protein production.

Definition of Exons

Exons are the coding part of the nucleotide sequence, which encodes for the amino acid sequence for the protein. These are the only parts, which are transcribed and converted into mature mRNA after post-transcriptional modification. These further moved to the cytoplasm, where they are translated into proteins, this happens with the support of another molecule known as tRNA.

Alternative splicing is helpful in promoting the different combinations of amino acids, by producing different combinations of exons and thus different proteins are formed.

Conclusion

The journey from the genes to the making of protein is complex and is performed with high fidelity to make the right and functional proteins. Though there are many confusing terms like the introns and exons, and their meaning is sometimes get interchanged.

From the above content, we conclude that till now the function of exons is very clear, but still, researches are going on to know much about the introns and their function in the nucleotide sequence.