Mature mRNA is a fully processed ___________.

hnRNA

The correct answer is Option (1) -hnRNA

Within the nucleus, there are at least three distinct RNA polymerases, aside from the RNA polymerase found in organelles, each with specific roles.

RNA polymerase I is responsible for transcribing ribosomal RNAs (rRNAs), including 28S, 18S, and 5.8S rRNAs.RNA polymerase III handles the transcription of transfer RNAs (tRNAs), 5S ribosomal RNA (5srRNA), and small nuclear RNAs (snRNAs).On the other hand, RNA polymerase II is tasked with transcribing the precursor of messenger RNA (mRNA), known as heterogeneous nuclear RNA (hnRNA).

The primary transcripts synthesized by RNA polymerases contain both exons (coding regions) and introns (non-coding regions) and are non-functional in this form. These primary transcripts undergo a crucial process known as splicing, during which the introns are removed, and the exons are joined together in a specific sequence.

hnRNA undergoes additional modifications, including capping and tailing, to become functional mRNA. In capping, an unusual nucleotide called methyl guanosine triphosphate is added to the 5'-end of hnRNA. In tailing, around 200-300 adenylate residues are added at the 3'-end in a template-independent manner. It is the fully processed mRNA that is subsequently transported out of the nucleus for translation. This processing and modification ensure that the mRNA is functional and capable of directing protein synthesis accurately.