What is meant by capping and tailing?

Explanation

hnRNA or heterogenous nuclear RNA is the precursor of mRNA modification at the 5' end of the primary RNA transcript (hnRNA) with methylguanosine triphosphate is called capping.
Purpose of capping
(i) Protects RNA from degradation
(ii) Capping plays an important role in removal of first intron in pre mRNA.
(iii) It regulates the mRNA export from the nucleus into the cytoplasm.
(iv) It helps in binding of mRNA to theribosome.
Tailing/Polyadenylation
The 3' end of hnRNA is cleaved by an endonuclease and a string of adenine nucleotides is added to the 3' end of hnRNA (pre mRNA) is known as Poly (A) tail - Polyadepylation. This process is called tailing or polyadenylation.
Purpose of tailing
(i) Translation of RNA transcript is facilitated.
(ii) Helps in the synthesis of polypeptides.
(iii) It enhances the mRNA stability in the cytoplasm.