Intron

Non-coding sections of an RNA transcript

For the protein, see Intron (protein).

Intron

An intron is a segment of a DNA or RNA molecule that does not code for proteins and interrupts the sequence of genes. Introns are found in the genes of most organisms and are removed by RNA splicing during the processing of the pre-mRNA into mature mRNA.

Structure and Function

Introns are non-coding regions interspersed within the coding regions, or exons, of a gene. During the process of transcription, both introns and exons are transcribed into a pre-mRNA molecule. However, before the mRNA can be translated into a protein, the introns must be removed. This removal is accomplished through a process called RNA splicing, which is carried out by a complex known as the spliceosome.

Types of Introns

Introns can be classified into several types based on their splicing mechanisms:

• Group I and Group II introns: These are self-splicing introns that can catalyze their own removal without the need for additional proteins or RNA molecules. Group I introns are found in some rRNA genes, while Group II introns are found in mitochondrial and chloroplast genes.

• Nuclear pre-mRNA introns: These are the most common type of introns in eukaryotic cells and require the spliceosome for their removal.

• tRNA introns: These are found in some tRNA genes and are removed by a different splicing mechanism involving specific endonucleases and ligases.

Role in Gene Expression

Introns play several important roles in gene expression and regulation:

• Alternative Splicing: Introns allow for alternative splicing, a process by which different combinations of exons are joined together to produce multiple protein variants from a single gene. This increases the diversity of proteins that can be produced by an organism.

• Regulation of Gene Expression: Introns can contain regulatory elements that influence the expression of the gene. These elements can affect the rate of transcription, the stability of the mRNA, and the efficiency of translation.

• Evolutionary Role: Introns may facilitate evolution by allowing for the recombination of exons, leading to the creation of new genes with novel functions.

Evolutionary Origin

The origin of introns is a subject of ongoing research and debate. Two main hypotheses have been proposed:

• Introns-early hypothesis: Suggests that introns were present in the earliest forms of life and have been lost in many prokaryotic lineages.

• Introns-late hypothesis: Proposes that introns were inserted into genes after the divergence of prokaryotes and eukaryotes.

Related Pages

• Exon
• RNA splicing
• Alternative splicing
• Gene expression
• Protein synthesis