Introns vs Exons
Introns and exons are frequently used terms in the field of molecular biology, but when someone starts to familiarize with these terms, the confusion would arise as both these are nucleotide sequences in genes or DNA strands. Although most of these terms are a little alien for the majority of the people, the understanding among people is becoming high about how the genes and DNA sequences define the characters of organisms. This article intends not only to explore the characteristics of introns and exons, but also to perform a comparison between the two to convey the information better.
Introns are sequences of nucleotides present in the genes between exons. These nucleotide sequences do not code for proteins, and that means introns are not immediately important for the process of protein synthesis. When a messenger RNA (mRNA) strand is created through transcription of DNA at a gene, the nucleotide sequence of introns is excluded. The exclusion of the intron sequence from the mRNA strand takes place through the process called RNA splicing; it could be through cis-splicing when there is only one intron incorporated with the gene, trans-splicing occurs when there are two or more introns associated with the gene. A mature mRNA strand, which is ready to code for a protein, is formed after removing the introns from the strand. Since both DNA and RNA contain these non-coding sequences, the term intron could be referred as the non-coding nucleotide sequences of DNA and their corresponding sequences in RNA.
It is important to notice that ribosomal RNA (rRNA) and transfer RNA (tRNA) contain genes with introns, but those are removed when the genes are expressed. In other words, introns go through transcription, but not through translation. Therefore, these are called untranslated sequences of DNA. The immediate function of introns is a little unclear, but it is believed that these are important to constitute for a diversified, yet related proteins from a single gene. Intron-mediated enhancing of gene expression has been accepted as another important function of introns.
Exons are the nucleotide sequences of genes that are expressed, and those are found at either sides of an intron. In simple terms, it could be stated that exons really hit the ground in the expression of genes or in the protein synthesis. The polypeptide strand is formed based on the nucleotide sequence in exons. When the mature mRNA molecule is formed through the transcription of DNA and then after RNA splicing takes place, it is a collection of exons.
Almost all the genes have an initial nucleotide sequence that distinguishes it as a gene from the main DNA or RNA strand, which is known as the Open Reading Frame (ORF); two ORFs mark the ends of a gene within those exons are located. Although it sounds that exons are always expressed in genes, there are some would not. There are instances where intron sequences intervene with the exon, to cause mutations, and this process is known as exonization.
What is the difference between Introns and Exons?
• Both are nucleotide sequences of genes, but exons are most often expressed while introns are silent.
• Exons are found at the two ends of a gene while introns are always found inside the gene.
• When mutations take place, introns sometimes contribute nucleotides but usually not the other way around.
• Both DNA and RNA contain introns and exons, but mature RNA only contain exons and not the introns.
• The immediate function of exons is to express the genes while it is unclear for the introns.