LIFE SCIENCE

Detailed explanation-1: -Unmodified RNA molecules synthesized first from the template DNA strand are called precursor mRNA (pre-mRNA) or heterogeneous nuclear RNA (hnRNA). This mRNA contains untranslated intervening sequences (introns). Introns interrupt the coding sequence and are excised from the pre-mRNA.

Detailed explanation-2: -heterogeneous nuclear RNA (hnRNA) An assortment of RNA molecules assembled around newly transcribed RNA (pre-messenger RNA, or pre-mRNA) in the cell nucleus. The hnRNA associates with proteins to form heterogeneous nuclear ribonucleoprotein (hnRNP).

Detailed explanation-3: -The hnRNA is the collective term for the unprocessed mRNA (pre-mRNA) molecules in the nucleus. It is largely comprised of the pre-mRNA molecules that require extensive processing to become mature mRNA molecules. The hnRNA that is associated with proteins form the heterogenous nuclear ribonucleoprotein (hnRNP).

Detailed explanation-4: -hnRNA undergoes additional processing claled as capping and tailing. In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5’-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3’-end in a template independent manner.