Give an account of post transcriptional | Class 12 Biology Chapter Molecular Basis of Inheritance, Molecular Basis of Inheritance NCERT Solutions

Post transcriptional Modifications:

The primary transcripts are non- functional that contains both the coding region, exon and non- coding region, intron in RNA and are called heterogeneous RNA or hnRNA. In eukaryotes, three types of RNA polymerases are found in the nucleus:

1. RNA polymerase I transcribes rRNA (28S and 5.8S)
2. RNA polymerase II transcribes the precursor of mRNA
3. RNA polymerase III transcribes tRNA, 5S rRNA and snRNAs.

The hnRNA undergoes two additional or main processes called capping and tailing.

In capping, an unusual nucleotide, methyl guanosine triphosphate is added to the 5’ end of the hnRNA. In tailing, adenylate residues about 200- 300 are added at the 3’ end in a template independent manner.

Now the hnRNA undergoes a process where the introns are removed and exons are joined to form mRNA by the process known as Splicing.