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

During elongation of polypeptide chain, sigma factor is

Transcription is a process by which

Prokaryotic transcription mechanism requires involvement of only one polymerase type and
$(a)$ It occurs in cytoplasm only
$(b)$ It is often coupled with translation
$(c)$ It does not require splicing but capping is essential

Explain (in one or two lines) the function of the followings:

$(a)$ Promoter

$(b)$ $tRNA$

$(c)$ Exons