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