Difference Between Exons and Introns, Definition and Function

Difference Between Exons and Introns: Exons are the parts of a gene that contain the instructions for making proteins, while introns are non-coding regions that interrupt the exons. Introns are only found in genes of eukaryotic organisms, which have a cell nucleus.

In eukaryotic cells, both introns and exons are copied into a molecule called mRNA during a process known as transcription. However, before the mRNA can be used to make proteins, the introns are removed, leaving only the exons in the mature RNA. The mRNA then leaves the nucleus and travels to the cytoplasm, where it is translated into a protein.

Exons and introns differ primarily in that introns remain in the nucleus to protect the DNA in genes, whereas exons leave the nucleus to be used in protein synthesis. The article below provides more information on the difference between exons and introns.

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Difference Between Exons and Introns Overview

Exons and introns are important components of DNA. Exons contain the protein-making instructions, whereas introns serve no specific function in protein production. The differences between exons and introns can be explained in three ways: size, function, and genomic location. DNA is composed of exons and introns. Exons are the components that make up genes, whereas introns are found at the start and end of genes.

DNA is made up of molecules called nucleotides. Each nucleotide contains a sugar (ribose or deoxyribose) and a nitrogenous base (adenine, guanine, or cytosine). Although the sequence of these bases appears to be random, it follows a pattern that allows cells in animals and plants to have identical DNA, despite their different structures. The length of DNA can differ between genes. DNA within a gene is typically either 30,000 bases long, 90% exons, or 21,000 bases, 90% introns.

Introns are DNA segments that are not required for the final structure of the gene. If an intron is removed from a chromosome, the resulting DNA piece will be shorter and unable to produce a functional protein. This can happen when there are chromosome duplications and one copy has an intron cut out by a transposon, but the other copy does not. The articles below detail the difference between exons and introns.

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Difference Between Exons and Introns

In eukaryotic genomes, exons and introns play important roles. Non-coding sequences called introns interrupt genes, whereas exons contain amino acid coding information.  Prokaryotic cells evolved into more complex eukaryotic cells. Eukaryotic cells are highly organized and more complex than prokaryotes. Despite prokaryotes' ability to evolve quickly, the intricate structure of eukaryotic cells is unparalleled. The table below shows the difference between exons and introns:

Exons

Exons are the regions of a gene that code for amino acids, which are the building blocks of proteins. They are found alongside introns in eukaryotic genes. After splicing, the mature RNA contains only the exons. Alternative splicing of exons allows different combinations of exons to be included in the final RNA, producing multiple proteins from a single gene. The entire set of exons in the genome is known as the exome, accounting for only a small fraction of the total genome. The majority of the genome is made up of introns and intergenic regions, which are segments of DNA that do not code for proteins. Exons are DNA regions that code for proteins and play a key role in protein diversity. The functions of exons include the following:

1. Protein Coding:

• Exons can code for different domains of a protein.
• A gene may be encoded by a single exon or a group of spliced exons.
• Exon shuffling with introns allows for molecular evolution and the formation of new genes.

2. Alternative Splicing:

• Alternative splicing in exons enables a single gene to produce multiple proteins.
• Exons can be arranged in various ways, including complete exon removal, partial exon, or intron inclusion.
• Alternative splicing can occur in the same gene location for different functional forms or cell or tissue types.

Introns

An intron is a piece of genetic material (DNA and RNA) that exists within a gene but does not contribute to producing the final protein. Introns can be found in both the gene and its initial RNA copy. The term "intron" means "in the nucleus," implying that they are separated from RNA in the nucleus. This removal process, known as RNA splicing, is a common feature of intron. As a result, the final RNA that exits the nucleus and goes on to produce proteins lacks introns.

Introns are divided into four categories: spliceosomal introns, tRNA introns, group I introns, and group II introns. Spliceosomal introns are found in protein-coding genes and are removed by the spliceosome. tRNA introns are transfer RNA segments that are removed during the maturation process. Introns in groups I and II can separate from RNA and form complex three-dimensional structures. Introns, previously considered "junk DNA," now have recognized roles in gene regulation and expression. They increase genetic diversity through crossing over, recombination, and alternative splicing. The functions of protein includes:

1. Introns increase the length of genes, which promotes crossing over and recombination between sister chromosomes.
2. Duplications, deletions, and exon shuffling involving introns contribute to genetic variation, leading to novel gene variations.
3. A single gene can encode multiple proteins through alternative splicing, which is made possible by introns. This process involves combining exons in different ways.
4. Introns contain spliceosome recognition sites, helping the spliceosome distinguish between introns and exons.
5. Small regions in the nucleolus recognize nucleolar ribonucleoproteins (snRNPs), which are components of the spliceosome. The spliceosome is a complex made up of various snRNPs that participate in mRNA splicing.

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