POST TRANSCRIPTIONAL MODIFICATIONS - EASY NOTES

• mRNA formed by the process of transcription is called primary transcript/ heteronuclear RNA/hn RNA
• It Undergoes extensive modifications to form mature RNA
• Post-transcriptional processing is not required in prokaryotes. The mRNA is functional immediately after synthesis.
• In eukaryotes, the process of post-transcriptional modification is much more complicated

The Post-Transcriptional modifications are :

1.     1.Poly A tailing :

• It occurs in the nucleoplasm
• The 3’end is polyadenylated ( addition of multiple adenine nucleotides)
• This poly a tail can be 20-250 nucleotides long.
• The polyadenylated tail protects mRNA from exonuclease activity

2.    2.Capping at 5’end:

• It occurs in the nucleus.
• The 5’end is capped with 7-methyl guanosine triphosphate.
• This process is useful in recognizing mRNA during translation.

3.    3.Methylation :

• It occurs in the cytoplasm
• The N6 of adenine and 2’hydroxyl group of ribose are methylated.

4.Removal of Introns & Splicing of Exons :

• It occurs in the nucleus.

• The primary transcripts formed are very long and have coding regions called exons and non-coding regions called introns.
• These non-coding regions(introns) are removed, and the coding regions(exons) are spliced together at the G-G residues.
• This process of removal of introns and joining of exons is energy-requiring.