Question

Capping is a process in which
(A) adenylate is added at the 5’ end
(B) methyl guanosine triphosphate is added at the 5’ end
(C) adenylate is added at the 3’ end
(D) methyl guanosine triphosphate is added at the 3’ end

Answer 1

Hint: Capping is a post-transcriptional process and is carried out along with tailing to protect mRNA. In the process of capping cap is added at 5'end and that cap is made up of methyl guanosine.
Step by step solution
After splicing mRNA undergoes simultaneous capping and tailing. As the word capping itself says it has to be done at the head or the starting of the molecule, similarly to the word tailing we can easily get an idea that it has to be done at the tail that is at the end of the molecule.
In tailing, adenylate residues (200-300), which are rich in adenine, are added at the 3’ end in a template-independent manner. In capping, an unusual nucleotide called methyl guanosine triphosphate, which is rich in guanine, is added at the 5’ end of hn RNA.
The fully processed hnRNA after the process of splicing, capping and tailing is now known as mRNA and now this mRNA is transported out of the cell for the process of translation. So from the above description, we can easily say that options (A), options (C) and options (D) are incorrect.
Hence option (B) is the correct answer
Note Please note that hnRNA has polarity that is one end of the strand is 5’ and the other end is 3’, the process of capping and tailing occurs basically simultaneously, so make sure that the end where capping has to occur is fixed and similarly the end where tailing has to occur is also fixed.