Question

Why are some untranslated sequences of bases seen in $mRNA$ coding for polypeptide? Where exactly are they present on $mRNA$?

Answer 1

The 5′ untranslated region (5′ UTR) (also known as a leader sequence or leader RNA) is the region of an mRNA that is directly upstream from the initiation codon. This region is important for the regulation of translation of a transcript by differing mechanisms in viruses, prokaryotes, and eukaryotes.