Give an account of post-transcriptional modifications of a eukaryotic $mRNA$.

(N/A) The primary transcripts $(hnRNA)$ contain both exons and introns and are non-functional. Hence,they undergo a process called splicing,where introns are removed and exons are joined in a defined order.
Introns are the portions of a gene that are transcribed but not translated.
In prokaryotes,$hnRNA$ is absent,so splicing is not required.
$hnRNA$ undergoes additional processing called capping and tailing.
In capping,an unusual nucleotide (methyl guanosine triphosphate) is added to the $5^{\prime}$-end of $hnRNA$.
In tailing,adenylate residues $(200-300)$ are added at the $3^{\prime}$-end in a template-independent manner.
It is the fully processed $hnRNA$,now called $mRNA$,that is transported out of the nucleus for translation.