1. In eucaryotes, most genes are interrupted: the coding
sequences (exons) are split by intervening sequences
(introns). Introns are removed post transcriptionally.

2. 1993 Nobel prize for Medicine – Discovery of split genes:
Richard Roberts Philip Sharp

3. Intron / Exon junctions are defined by a specific sequence
at the 5’ terminus (beginning) and 3’ terminus (end) of the
intron.
Introns ALWAYS begin with GU and end with AG;
the GU / AG rule

4. The intron exon junctions are recognised by a collection
Of 5 small nuclear RNAs (snRNA) and 50 proteins
which form the spliceosome (snRNPs) “SNURPS”

5. Spliceosomes recognise junctions and cleave 5’intron end;
Intron loops to itself to form a “lariat”
3’ intron end is cleaved and intron is degraded.

6. Thalassemia, a form of anaemia common in Mediterranian
countries, is caused by errors in the splicing process.
Normal red blood cells contain correctly spliced
beta-globin, an important component in hemoglobin
that takes up oxygen in the lungs.

7. The red blood cells in thalassemia patients are distorted and
immature, containing a nucleus. This is due to a point mutation in the beta-globin gene, which causes an error in splice site selection. A faulty beta-globin protein is made, leading to severe anemia.
Aberrant
Normal

8. A percursor-RNA may often be matured to mRNAs with alternative
structures.An example where alternative splicing has a dramatic
consequence is somatic sex determination in the fruit fly... It controls
a cascade of alternative RNA splicing decisions that finally result
in female flies.

9. WHY is splicing a feature of eucaryotes and not procaryotes?
Two theories :
Intron early
The earliest progenote had a spliced genome
Intron late
Progenote was unspliced, and introns were inserted later

10. Intron early Intron late The earliest progenote had a spliced genome
Archaebacteria still have spliced genes.
Eubacteria do not and have “streamlined” their genome.
Intron late
Progenote was unspliced, and introns were inserted later
Intron insertion would have destroyed coding genes

13. Is exon shuffling of any benefit to the eucaryotic organism?
It allows the generation of new proteins