Difference Between Exons and Introns (With Table)

The nucleotide sequences present in a gene are of two types, exons and introns. They are responsible for protein synthesis Within a gene. Sometimes the non-coding regions interrupt the coding regions. In this article, we will understand the key terms exons, introns, and the difference between exons and introns.

Exons vs Introns

The main difference between exons and introns is that exons require information or codons for the synthesis of proteins and are sequences of DNA that code protein, whereas Introns are sequences of DNA that do not code and are separated during RNA maturation through the process of splicing of RNA.

Exons code different types of proteins by different sequences that are formed via different configurations by the process of combination of exons. It is a part of a gene that encodes one or more parts of the produced mature RNA after the removal of introns by the process of RNA splicing. The DNA sequence present within a gene and it’s the corresponding sequence that is present in transcripts of RNA describes the term exon.

Introns are the nucleotide sequences that are removed by the process of splicing of RNA when the final product of the RNA matures. An intragenic region within a gene is well described as an intron. Introns have the capability of converting into novel genes throughout the evolutionary process of the non-coding short regions that convert into real functional genes.

Comparison Table Between Exons and Introns

Parameters of comparisonExonsIntrons
Sequence typeExons code specific proteins and are protein-coding sequences.Introns do not code and are non-coding sequences.
Found inExons are found in both prokaryotic and eukaryotic organisms or genomes.Introns are found in a single-celled organism or eukaryotic organism only.
Present inMature RNAs, mRNA transcripts, DNA.mRNA transcripts, DNA but not in mature mRNAs.
Protein SynthesisExons synthesize and are involved in protein synthesis.Introns do not synthesize proteins.
QuantityExons are available in lesser quantity in a genome.Introns are available in higher quantities.
Human genome compositionThe human genome constitutes 1% of exons.The human genome constitutes 24% of introns.

What are Exons?

The DNA sequences that code protein are called Exons. However, they require some information or the codons that are necessary for the synthesis of proteins. The region that ks expressed in the genome is termed as an exon. In eukaryotic organisms, the exons that code are separated by the introns. The exosome is the total sets of exons that are present in the genome of an organism.

The removal of introns that are present in between the exons leads to the coding of messenger RNA or mRNA during the splicing of RNA. After the process of transcription, both introns and exons occurred in the resulting RNA. While RNA splicing, the introns are removed, producing mature messenger RNAs. This mature messenger RNA that gets transcripted has untranslated regions along with exons. In the entire sequence, exons forming a small part.

Exons are not limited to a few organisms. They are present in organisms like viruses to jawed vertebrates. One percent of the whole human genome is constituted of exons and intergenic DNA. Introns occupy the rest. Exonization is the process in which introns are sometimes converted into exons. Exons hold much importance in the protein synthesis process. Exons carry codons and code various protein molecules.

Exons are responsible for the coding of proteins and especially the sequence of amino acids. The conservation of exons and the sequences are high. As the exons and their sequence with times do not change. Exons are excessively present in messenger RNA.

What are Introns?

When RNA product matures within a gene, the non-coding sequences of DNA are separated by RNA splicing. Those are called Introns. The intragenic region that is present in a gene represents Intron. Introns are responsible for showing that, within a gene, the existing DNA sequences transcripts with the corresponding RNA sequence.

Introns are generally found in organisms comprising of multiple cells, that is, eukaryotic organisms. These are also found in various viruses and genes. Transfer RNA, ribosomal RNA, generates proteins and includes introns in them. Prokaryotic organisms or the organisms having single-cell lack introns.

However, in eukaryotes, Introns are generally found in the intervening area between two Exons. Introns specifically undergo the splicing process as they are not capable of coding the proteins directly. Even before the mRNA makes proteins, these introns are removed. The conservation of introns is a very challenging task. Therefore their removal is necessary so that the incorrect protein formation can be prevented.

Introns can vary according to the analysis of their sequence, genes, and biochemistry of splicing methods of RNA. The existence, survival, and sustenance of Introns require a high amount of energy. They start burdening some cells due to their high consumption of energy. They need the energy to imitate and excise at the correct position exactly via some complicated techniques such as the spliceosomal technique.

Main Differences Between Exons and Introns

  1. Exons are present in between two introns of two untranslated regions or one Intron and one untranslated region whereas, Introns are present in a DNA sequence in between two exons.
  2. Exons are strictly found in both multi-celled and single-celled organisms and genomes whereas, introns are found only in single-celled organisms and genomes.
  3. Exons separate the nucleus to the cytoplasm after the synthesis of mature messenger RNA whereas, Introns do not leave the nucleus during the processing of RNA even after the splicing of the messenger RNA transcription.
  4. Exons within a cell can be found in mRNA transcripts, DNA, mature RNAs. Whereas introns, within a cell, can be found out in messenger RNA transcripts, DNA but not in mature messenger RNAs.
  5. In exons, the sequence is conserved highly and is not subjected to frequent changes, whereas by exonization, some introns get converted into exons.
  6. Inside the nuclear genome, the quantity of exons present is less. However, the introns are present in higher quantities.
  7. Through the process of alternative splicing, Exons, two or more in number are connected, and introns are removed.

Conclusion

The presence of both coding and the non-coding sequences within a gene is of utmost importance. Exons and Introns mutually work and help in the synthesis of important proteins and information within a gene. Exons are the coding regions, whereas introns are the non-coding regions present in a gene. While the introns are important as they help in gene regulation and expression, the exons are important for encoding proteins.

References

  1. https://www.sciencedirect.com/science/article/pii/0014579387800029
  2. https://content.iospress.com/articles/in-silico-biology/isb00142