(i) Name the enzyme that catalysis the transcription of hnRNA. (ii) Why does the hnRNA need to undergo changes? List the changes hnRNA undergoes and where in the cell such changes take place?

Explanation

(i)RNA polymerase II
(ii) Because it contains both the exons and the introns and is non-functional Hence, it is subjected to a process called splicing where the introns are removed and exons are joined in a defined order. RNA undergoes two additional processings called capping and tailing In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5'-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3'- end in a template independent manner. These all changes occur inside the nucleus and finally the fully processed, hnRNA now called mRNA is transported out of the nucleus for translation