Definition of Introns and Exons
Introns and exons are segments of DNA within a gene that are transcribed into RNA. Exons are the coding regions, meaning they contain the genetic information that will be translated into protein. Introns, on the other hand, are non-coding regions that are typically removed before protein synthesis.
Role in Gene Expression
During gene expression, the entire gene, including both introns and exons, is initially transcribed into a precursor messenger RNA (pre-mRNA) molecule. For this pre-mRNA to become a mature messenger RNA (mRNA) that can be translated into a protein, the introns must be precisely excised, and the exons ligated (joined) together in a process called RNA splicing.
Example in Eukaryotic Cells
Consider a typical gene in a human cell. After transcription, the pre-mRNA contains several exons interrupted by introns. Specialized molecular machinery, known as the spliceosome, identifies these intron sequences, cuts them out, and then stitches the remaining exon sequences together. This processed, mature mRNA then exits the nucleus to be translated into a specific protein.
Importance of Splicing
The accurate removal of introns through splicing is vital for producing functional proteins. Furthermore, alternative splicing, where different combinations of exons are joined, allows a single gene to code for multiple distinct protein isoforms. This significantly expands the functional diversity of proteins that an organism can produce, playing a key role in cellular regulation and organismal complexity.