Exon

Exon is a term in genetics that refers to a sequence of DNA or RNA which codes information for protein synthesis. In other words, exons are the portions of a gene that are expressed (i.e., translated into a protein). They are interspersed with non-coding sequences, known as introns, which are removed during the process of RNA splicing.

Overview

The term "exon" was first coined in 1978 by American biochemist Walter Gilbert to refer to both the expressed region of a DNA sequence within a gene and the corresponding sequence in RNA molecules. The definition of an exon remains a matter of debate among scientists, but it is generally accepted that an exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule.

Structure and Function

Exons can be as short as two nucleotides or as long as several thousand. They are typically separated by introns, non-coding regions of DNA that do not contribute to the final protein product. During the process of RNA splicing, these introns are removed, and the exons are joined together to form a contiguous coding sequence.

Exons play a crucial role in the production of proteins, which are essential for the growth and repair of body tissues and the production of enzymes and hormones. They also play a role in the regulation of gene expression and the evolution of proteins.

Exon Shuffling

Exon shuffling is a molecular mechanism that may contribute to the evolution of new proteins. It involves the recombination of exons within a gene or between genes, which can lead to new combinations of protein domains.

Exon Skipping

Exon skipping is a form of RNA splicing used by cells to regulate gene expression. It involves the skipping of an exon during the splicing process, resulting in a protein with an altered amino acid sequence.

Clinical Significance

Mutations in exons can lead to various genetic disorders. For example, Duchenne muscular dystrophy is caused by a mutation in the dystrophin gene that disrupts the reading frame, leading to an absence of the dystrophin protein. Similarly, Cystic fibrosis is often caused by a three-nucleotide deletion in the CFTR gene that results in the loss of a phenylalanine residue.

See Also

• Intron
• Gene
• Protein synthesis
• RNA splicing
• Exon shuffling
• Exon skipping

References

Exon Resources
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