POST TRANSCRIPTION It is a set of biological processes common to most eukaryotic cells. WOBBLE HYPOTHESIS is the base pairing that occurs between nitrogen bases.

1. POST TRANSCRIPTIONAL
MODIFICATION
&
WOBBLE HYPOTHESIS
SUBMITTED BY
A. FAHEEMA RASOOL
I Msc MICROBIOLOGY
SUBMITTED TO
MS.K. KANAGA
ASSISTANT PROFRESSOR

2. POST TRANSCRIPTIONAL MODIFICATION
• It is otherwise called as co-transcriptional modification.
• It is the process in eukaryotic cells where primary transcript RNA is
converted into mature RNA.
• A notable example is the conversion of precursor mRNA into
mature mRNA that occurs prior to protein translation.

3. STEPS OF mRNA PROCESSING
5’ capping formation
3’ polyadenylation
RNA splicing

4. POST TRANSCRIPTIONAL MODIFICATION

5. 5’ CAPPING FORMATION
• The 5’ end of the pre- mRNA is altered by the attachment of
guanosine nucleotide via the special link 5’-5’- triphosphate
linkage.
• The guanosine nucleotide quickly methylated at the 7’ position
to form 7- Methyl guanosine.
• One important function of this cap is to protect mRNA from
degradation during protein synthesis.

6. 5’ CAPPING FORMATION

7. 3’ POLYADENYLATION
• The 3’ end of pre- mRNA is removed and a series of
adenosine nucleotide are added.
• The 3’ end tail that contains many adenines called poly (A)
polymerase (PAP), which contains 250 nucleotides.
• The poly (A) tail also provides the mRNA with stability and
keeps the tail from degrading.

8. 3’ POLYADENYLATION

9. RNA SPLICING
• Splicing is the editing of the nascent pre- mRNA into a mature
mRNA.
• Splicing is catalysed by the spliceosome.
• Not all regions of the pre- mRNA molecule code for proteins.
The regions that do code for proteins called exons.
• Before the pre- mRNA exits the nucleus, special protein will
cut out the introns and splice together the exons.
• SnRNA is the important protein molecule present in it.

10. RNA SPLICING

11. WOBBLE HYPOTHESIS
• Wobble hypothesis is different variation of basepair between
the different base analogs in RNA.
• Crick (1996), proposed the wobble hypothesis to explain the
degeneracy of the genetic code.
• There are 61 codons that synthesize aminoacid. Each codons
have particular aminiacid.
• The total number of tRNAs is less than 61.

12. • According to the wobble hypothesis only the first and second
base of the triplet codon on 5’- 3’ mRNA pair with the bases of
the anticodon of tRNA.
• The conventiomal pairing (A=U), (G=C) is known as watson-
crick pairing and the second abnormal pairing is called wobble
pairing.
• The anticodon of yeast alanine- tRNA contains the nucleoside
inosine.

13. ANTICODON
tRNA
CODON
mRNA
A U
C G
G C/ U
U A/ G
I A/ C/ U
• Due to the wobble base pairing one tRNA becomes able to
recognise more than one codons for an individual aminoacid.

14. DNA triplet, mRNA codons and tRNA anticodons showing
watson- crick pairing.

15. Wobble pairing of one glycine tRNA with three codons of
mRNA due to wobble in 5’ 3’ direction.