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. (Don't confuse 'splicing'
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
Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2014 by Steven M. Carr