Desrcribes the structure of precursor mRNA or Primary Transcript as a first formed product of transcription.

1. RNA Processing
Primary transcript
RASHMI PANDEY
ASSISTANT PROFESSOR
SATHAYE COLLEGE
MSC PART – II
PAPER II UNIT III
30-08-2020 RASHMI PANDEY

2. The formation of functionally active mRNA is the consequence of
a complex series of steps:
The actual transcription of DNA into mRNA precursors
The intranuclear processing of these presursors
The transport of mRNA into the cytoplasm and subsequent association
with Ribosomes for translation
30-08-2020 RASHMI PANDEY

3. HETEROGENOUS NUCLEAR RNA ( hnRNA)
The hnRNA is the collective term for the unprocessed RNA molecules
in the nucleus.
It is largely comprised of the pre-mRNA molecules that require
extensive processing to become mature mRNA molecules.
Although the hnRNA serve as precursor of mRNA, not all hnRNA
become cytoplasmic mRNA.
30-08-2020 RASHMI PANDEY

4. PRIMARY TRANSCRIPT
The First draft transcribed from the DNA is as a Precursor
mRNA ( Pre mRNA) or Primary transcript which ultimately
gives rise to mature mRNA after excessive processing
30-08-2020 RASHMI PANDEY

5. DNA
RNA
5’UTR 3’UTREXON 1 EXON 2 EXON 3 EXON 4
INTRONINTRONINTRON
30-08-2020 RASHMI PANDEY

6. 5’ UTR
• The region of RNA at the 5’ end which does not gets translated into a
protein.
• Never-coded region
• Has a site or signal for 5’ capping
• Approximately 50 nucleotide long
• Has a ribosomal binding site
• It is called as 5’ untranslated region (5’UTR)
30-08-2020 RASHMI PANDEY

7. 3’ UTR
• The region of RNA at the 3’ end which does not gets translated into a
protein.
• Never-coded region
• Variable in size from approx. 100 nucleotide to almost 600
nucleotides long present in ovalbumin mRNA
• Has a site or signal for 3’ polyadenylation – addition of poly A tail
• The conserved sequence AAUAAA for polyadenylation is invariably
present in all mRNAs
• It is called as 3’ untranslated region (3’UTR)
30-08-2020 RASHMI PANDEY

8. EXONS
• An exon is the portion of a gene that codes for amino acids.
• They are many times in the form of pieces interspersed with the
non-coding region called introns.
• In single primary transcripts number of exons could be present.
30-08-2020 RASHMI PANDEY

9. INTRONS
Are the sequences present in between the exons or the coding
regions of the mRNA
Are also called as intervening sequences
Sizes range from a short 50-100 bps to upto 600 bps or even of a size
of mature mRNA
30-08-2020 RASHMI PANDEY

10. INTRONS
Number also varies from few to multiple as in 7 in ovalbumin and
upto 40 in case of collagen.
Are the non-coding regions of pre-mRNA and never part of mature
RNA
Are exicised from mRNA in a process called splicing before a mRNA is
transported to cytoplasm
30-08-2020 RASHMI PANDEY

11. Pre mRNA or Primary Transcript
30-08-2020 RASHMI PANDEY

12. 30-08-2020 RASHMI PANDEY