Primary Transcript

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 R NA 5’UTR 3’UTR EXON 1 EXON 2 EXON 3 EXON 4 INTRON INTRON INTRON 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’ u n t ranslated r egion (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’ u n t ranslated r egion (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. THANK YOU MEET AT THE NEXT SESSION 30-08-2020 RASHMI PANDEY