This document summarizes RNA splicing. It begins with a brief history of the discovery of RNA splicing and defines key terms like intron, exon, and spliceosome. The main part of the document describes the process of RNA splicing, where the spliceosome removes introns from pre-mRNA and joins the exons to produce mRNA. Finally, it discusses some applications of RNA splicing in gene expression, protein diversity, and cancer.

1. JABALPUR (M.P.)
(AUTONOMOUS)
SESSION – 2020-2021
SUBJECT
RNA Splicing
SUBMITTED TO
Department of Zoology
SUBMITTED BY
Vaishali Choudhary
M.Sc I Sem.

2. SYNOPSIS
History
Definition
What is intron?
What is exon?
What are spliceosome?
Process/Mechanism
Types of RNA splicing
Application
Conclusion

3. HISTORY
RNA splicing was discovered by two scientists
Phillp Allen Sharp and Richard J. Roberts and
they were awarded the 1993 Nobel Prize in
Physiology or Medicine for their achievement.

4. INTRODUCTION
The word 'splice' - means to join.
Removal of Introns & joining of exon.
Commonly observed in eukaryotes.
Exon and Intron are present alternate manner.
Every molecule start with an exon and end with exon.
The process of cutting the pre-MRNA to remove the
introns and joining together of the exons is called
splicing.
It takes place in the nucleus before the mature MRNA
can be exported to the cytoplasm.
 Most genes have their protein-coding information
interrupted by non-coding sequences called "introns".
The coding sequences are then called "exons".
 Introns: non-coding sequences.
 Exons: coding sequences.

5. “RNA splicing is a process that removes the intervening,
non-coding sequences of genes (introns) from pre-mRNA
and joins the protein-coding sequences (exons) together in
order to enable translation of mRNA into a protein.”

6. INTRONS
Introns are nucleotide sequences in DNA and
RNA that do not directly code for proteins, and
are removed during the precursor messenger
RNA (pre-mRNA) stage of maturation of mRNA
by RNA splicing.
Introns can range in size from 10’s of base
pairs to 1000’s of base pairs, and can be found in
a wide variety of genes that generate RNA in
most living organisms, including viruses.
Introns are non-coding DNA sequences
present within a gene that are removed by the
process of RNA splicing during maturation of
the RNA transcript.

7. EXONS
Exons are protein-coding DNA sequences that
contain the necessary codons or genetic
information essential for protein synthesis.
Exons usually include both the 5’- and 3’-
untranslated regions of mRNA, which contain
start and stop codons, in addition to any protein
coding sequences.
Exons are found in all organisms ranging from
jawed vertebrates to yeasts, bacteria, and even
viruses.
Exons are essential units in protein synthesis as
they carry regions composed of codons that code
for various proteins.

9. SPLICEOSOME
RNA splicing is carried out by this large complex or
huge molecular machinery called the spliceosome.
It is a large and complex molecular machine which helps
to remove the introns from pre-Mrna molecule
The combination of RNAs with these proteins results in
the formation of an RNA-protein complex termed as small
nuclear ribonucleoproteins (snRNPs).
These are mostly confined within the nucleus where they
remain associated with the immature pre-RNA transcripts.
The spliceosome functions as an editor that selectively
cuts out unnecessary and incorrect materials (introns) to
produce a functional final-cut.
All spliceosomes are involved in both the removal of
introns and the ligation of remaining exons.

10. The complexes of snRNA and proteins are called small nuclear
ribonuclear proteins (snRNP, pronounces "snurps"). There are 5
snrnp's U1, U2, U4, U5, U6

11. RNA Splicing Process/ Mechanism
 The process of RNA splicing begins with the binding
of the ribonucleoproteins or spliceosomes to the introns
present on the splice site.
 The binding of the spliceosome results in a biochemical
process called transesterification between RNA
nucleotides.
 During this reaction, the 3’OH group of a specific
nucleotide on the intron, which is defined during
spliceosome assembly, causes a nucleophilic attack on the
first nucleotide of the intron at the 5’ splice site.
 This causes the folding of the 5’ and 3’ ends, resulting
in a loop. Meanwhile, the adjacent exons are also brought
together.
 Finally, the looped intron is detached from the
sequence by the spliceosomes.
 Now, a second transesterification reaction occurs
during the ligation of adjacent exon segments.

12.  In this case, the 3’OH group of the released 5’ exon then performs
an electrophilic attack on the first nucleotide present just behind the
last nucleotide of the intron at the 3’ splice site.
 This causes the binding of the two exon segments along with the
removal of the intron segment.
 Earlier, the intron released during splicing is thought of as a junk
unit. Still, it has been recently observed that these introns are involved
in other processes related to proteins after their removal.
Besides the spliceosomes, another group of protein/ enzymes termed
‘ribozymes’ are also involved in the control and regulation of the
splicing process.

16. RNA Splicing Application
There are various biological, medical applications associated with
pre-mature RNA splicing, some of which are:
Pre-mRNA splicing is a fundamental process in cellular
metabolism that plays an essential role in generating protein
diversity.The diversity is brought about by changes in the number
and sequence of exons and introns present in the RNA sequence.
RNA splicing also helps in the regulation of gene and protein
content in the cell.
Splicing of RNA sequences assists the process of evolution of new
and improved proteins.
Various aberrant splicing isoforms act as markers for cancer and as
targets for cancer therapy.
Pre-mRNA splicing is a key to the pathology of cancers where it
regulates the three functional aspects of cancer: proliferation,
metastasis, andapoptosis.

17. CONCLUSION
Sequences removed are called Introns.
Coding sequences flanking introns are called
exons.
Exons are not removed and are in the mRNA.
Intron removal is referred to as Splicing.
Splicing is mediatod by a particle: Spliceosome.
A spliceosome is made of snRNA and protein.
There are several snRNAs in a spliceosome , U1 to
U6.
Some introns have self - splicing sequences :
Ribozymes.

18. References
https://en.wikibooks.org
https://www.sciencedirect.com
https://www.news-medical.net
https://microbenotes.com/rna-splicing/

19. Thank You