An important note on the terminology of Splicing of Exons & Introns
definition of 'splicing' is the joining
of two things, for example the ends of two ropes. It
should not be confused with 'splitting', which is separating
two things. However, in molecular biology, ''splicing out'
refers to the removal of some RNA segments in the process of splicing together
the remaining segments.
The terms and 'exon' and 'intron' properly refer to regions of the DNA. that are respectively "expressed" and "intervening." However, these terms are sometimes used loosely to refer to the corresponding sequences in hnRNA that are rerained or removed, respectively, from the final mRNA product. These should properly be called intron & exon transcripts, as in the above diagram. 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.
Avoid thinking of splicing as splitting of the hnRNA transcript. Avoid thinking of exons as the translated portions of the mRNA. In the figure above, the phrase "Splicing eliminates intron transcripts" means that "Splicing, by joining together the exon transcripts, results in the elimination of intron transcripts," not that splicing is the direct elimination of intron transcriptss.
Figure © 2000 by Griffiths et al. ; text © 2013 by Steven M. Carr