What are introns and exons?
In addition, consider this:
Splicing machine: The film editing analogy
In a fascinating essay titled “The Alternative Genome” (Scientific American, April 2005), Gil Ast describes the genetic “splicing machine.” Reversing the analogy from the 1920s proposed by the great Soviet filmmaker Sergei Eisenstein, who compared the creative force of “dialectic montage” with the generative power of the human cell, Ast uses a metaphor from film editing to account for the generative power of genes. He explains that 25 years ago we discovered cells can give rise to very different forms of protein from a single gene — a process we assumed was rare. But now we realize how widespread alternative splicing is in complex organisms.
The RNA transcripts of genes that encode a protein are ultimately read by cellular machinery and translated into a corresponding linear sequence of amino acids (like building a sentence or narrative). It was earlier assumed this process involved only the pruning away of introns (those “nonsense chapters”) from the RNA transcripts, leaving only exons (the “meaningful chapters”) as building blocks to tell “a coherent story”— a binary system of splicing analogous to traditional forms of editing. But now we know the cellular machinery is more complicated.
For, like Eisenstein’s “dialectic montage” (where both presence and absence are significant and where the whole is greater than the sum of the parts), alternative splicing can cut out an intron or an exon, and recombine pieces of either. It is the particular remix that generates new forms. This editing ability, Ast argues, “significantly increases any gene’s versatility and gives the splicing mechanism tremendous power to determine how much of one type of protein a cell will produce. In other words, it allows humans to manufacture more than 90,000 proteins without having to maintain 90,000 genes.”
And it helps explain why, mice and men can have such similar genomes, and still be so vastly different from each other.
— Marsha Kinder