iGen3 05-12

Post-transcriptional processing of RNA in Eukaryotes

[An important note on terminology: Splicing of Exons & Introns]


    The terms 'exon' and  'intron' refer to expressed and intervening DNA sequences, respectively. However, as in the above diagram, they are sometimes used to refer to the corresponding sequences in hnRNA that are retained or removed, respectively, from the final mRNA product. This is technically incorrect: these should properly be called intron and exon transcripts. This means of course that the sequences of the DNA exons in the sense strand are identical to the corresponding mRNA exon transcripts, except for substitution of U for T. Thus the corresponding amino acid sequences can be either 'read' directly from the DNA sense strand, or 'translated' from the mRNA.

    Similarly, 'splicing' involves the joining of two things, for example the ends of two ropes. It should not be confused with 'splitting'. In molecular biology, splicing refers to the process of joining exon transcripts, during which intron transcripts are removed, which process is often referred to as 'splicing out'.

Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2012 by Steven M. Carr