Intron

An intron is a non-coding region of DNA within a gene that is transcribed into pre-mRNA, but is removed by RNA splicing during the processing to mature mRNA. Introns are therefore not present in the final mRNA molecule and are not translated into protein. They are found in genes in most eukaryotes and in some viruses, but are rare in prokaryotes.

Key Characteristics:

• Non-coding: Introns do not directly encode amino acid sequences.
• Transcription: They are transcribed into pre-mRNA along with exons (coding regions).
• Splicing: Introns are removed from pre-mRNA during RNA splicing.
• Eukaryotes: More prevalent in eukaryotes compared to prokaryotes.
• Variable Length: Intron size can vary significantly, even within the same gene or between different genes.

Function and Significance:

While traditionally considered "junk DNA," introns are now understood to play various roles in gene expression and genome evolution. These roles include:

• Alternative Splicing: Introns allow for alternative splicing, where different combinations of exons can be joined together to produce multiple protein isoforms from a single gene. This increases the diversity of the proteome.
• Gene Regulation: Some introns contain regulatory sequences that influence gene transcription or mRNA stability.
• Evolution: Introns may facilitate genetic recombination and the evolution of new genes by providing regions for insertions and deletions without disrupting coding sequences.
• Exon Shuffling: Introns can facilitate exon shuffling, a process where exons from different genes are combined to create new genes.

Comparison to Exons:

Exons are the coding regions of a gene that are retained in the mature mRNA and translated into protein. In contrast to introns, exons contain the information necessary for protein synthesis. The process of RNA splicing removes introns and joins exons together.