this explains the modification of RNA in eukaryotes

1. Asst. Prof. R. M. Mahindrakar
Botany Department
J.S.S. Arts, Science and Commerce College Gokak

2. Post Transcriptional Changes

3. mRNA Processing
1. Capping (addition of a 5’ 7-methyl guanosine cap)
2. Polyadenylation (addition of a poly-A tail at the 3’)
3. Splicing to remove intervening sequences (introns)

4. Process of Capping:

5. Cap Functions
Cap provides:
1. Protection from some ribonucleases degradation
2. Stabilizes mRNA
3. Enhanced translation and splicing
4. Enhanced transport from nucleus to cytoplasm

6. Addition of Poly –A Tail

8. Functions:
 The Poly A tail also provides stability
 It facilitate the exit of mRNA from the nucleus.
 After the mRNA enters the cytosol , the poly A tail is
gradually shortened

9. Splicing

10. Splicing

15. EXON SHUFFLING
 Some genes have exons that can be exchanged by a process
called exon shuffling.
 For example a gene with four exons might be spliced
differently in two different cell types
 In Cell type 1 : exons 2 and all introns are spliced resulting
into a protein with 1,3 and 4 exons.
 In Cell type 2 : exons 3 and all introns are spliced resulting
into a protein with 1,2 and 4 exons.
 Thus different protein types will be produced by two cell
types
 This phenomenon is known as Exon shuffling.

17. Processing of tRNA
 Removal of leader sequence & trailer
 Replacement of nucleotide
 Modification of certain bases:
 Splicing of an intron

19. Processing of ribosomal RNA
 Processing of 45s molecules occurs inside nucleolus
 45s molecules tightly associated protein forming
(RNPs)
 First cleavage: It occurs at site I & remove 5’ terminal
leader sequence, produces 41s intermediate & 18s
 Second cleavage: occurs in 41s intermediate at site 3’
generates 32s intermediate
 Final cleavage: separation of 32s intermediate into 28s,
5.8s
 Processed rRNA 28s, 5.8s & 18s