Introns vs. Exons

Genetic information flows in the living things by the synthesis of DNA and RNA. DNA makes RNA, and then RNA synthesizes proteins. These processes are Replication, Transcription, and Translation. In Replication, DNA or deoxyribose nucleic acid are copied to generate an identical copy of the DNA molecule. After this step, Transcriptions starts in which ribonucleic acid is synthesized from the DNA. In the final step, stored genetic information is expressed in proteins form, which is called translation.

In transcription, where the entire DNA is copied into pre-mRNA and sequences are present, which are made up of non-coding regions or introns and coding regions or exons. Pre-mRNA undergoes many modifications, which are called post-transcriptional changes. In these modifications, introns are removed, and exons are joined to produce a specific sequence. These processes are used to convert pre-mRNA into its active form called mature mRNA, which is ready for translation.

Introns are also known as an intervening sequence, and these are the non-coding part of the genes, whereas exons, also known as an expressed sequence, are the coding part for proteins of the genes. American biologists Richard Roberts and Phillip Sharp discovered introns and exons in 1977. Introns are the common characteristic parts of multicellular eukaryotes, whereas exons are found in both eukaryotes and prokaryotes. Prokaryotes have no nucleus, so exons are used as genes, whereas eukaryotes are both single and multi-celled organisms.

Comparison Table

Basis for ComparisonIntronsExons
DefinitionIntrons can be defined as the segments of DNA or RNA that do not provide information for coding and interrupts the sequence of genes.Exons can be defined as the segments of DNA or RNA containing information for the coding of proteins or peptide sequences.
DiscovererRichard Roberts and Phillip SharpRichard Roberts and Phillip Sharp
Other namesIntervening sequenceExpressed sequence
Found inEukaryotesProkaryotes and eukaryotes
Part ofNon-coding sequenceCoding sequence
FunctionTo synthesize proteinsTo synthesize proteins

What is Introns?

An intron is a nucleotide sequence in DNA and RNA. These are the interrupting or intervening sequences present between the two exons. They are found in eukaryotic organisms, such as in humans. They range from 10 to 1000 base pairs. These sequences do not code for proteins directly but are the parts of transcribed pre-mRNA. Introns are removed before the mRNA converts into the proteins during the process of splicing.

RNA splicing is one of the steps of post-transcriptional modification for the removal of introns. This step is supported by small nuclear ribonucleoprotein particles (snRNPs). These snRNPs are produced with the association of the small nuclear RNA with proteins. They are called spliceosomes jointly. Splicing occurs at specific sites, and they begin with the nucleotides present as GU at 5 ends and AG at the 3 terms. These bind at both ends of the introns and form the loop and then introns are removed, and exons are joined. Modifications occur in the nucleus in the nucleus after which the mature RNA moves to the cytosol to perform the function of translation.

What is Exons?

Exon is the coding area of the nucleotide sequence, which provides codes for the amino acid sequence for the proteins. These are the parts that are transcribed and converted into mature mRNA after post-transcriptional modification. Then they are moved to the cytoplasm where they are translated into proteins. This process happens with the help of a tRNA molecule. Alternative splicing is useful in promoting the different combinations of amino acids by producing different combinations of exons that are helpful in producing different proteins. Alternative splicing can take place on the same site to create different variants of a gene with a similar role. For example, the human slo gene, or can occur in different cells or tissues such as the mouse alpha-amylase gene. Imperfections in alternative splicing can result in different diseases, including cancer and alcoholism.

Key Differences between Introns and Exons

  1. Introns are non-coding areas, whereas exons are a coding area.
  2. Introns are called a nucleotide sequence within the genes that are removed through RNA splicing for producing a mature RNA, whereas an exon is called a nucleic acid sequence, which is expressed in the RNA molecule.
  3. Introns are less conserved, which means their sequences change very frequently over time, whereas exons are very much conserved.
  4. Introns are not all implicated with the protein-coding, whereas exons are codes of proteins.
  5. Introns are DNA bases that are found in between exons, whereas exons are DNA bases that are translated into mRNA.
  6. Exons are present in both prokaryotes and eukaryotes, whereas Introns are found only in eukaryotes.

Key Similarities between Introns and Exons

  • Both introns and exons are involved in protein synthesis.


In sum, both introns are exons are an essential part of sequences that play a role in protein synthesis. Introns are the non-coding and exons are the coding parts of genes.

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