Rna splicing

RNA splicing

1. ST. ALOYSIUS COLLEGE 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.

8. 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 .

9. 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

10. 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.

11. 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.

12. 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 .

13. 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 .

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

15. Thank You