Question

How is transcription a more complex process in eukaryotic cells? Explain the additional processes that a precursor mRNA has to undergo in these organisms.

Answer 1

1. Transcription in eukaryotes involves one of three types of polymerases, depending on the gene being transcribed. RNA polymerase II transcribes all of the protein-coding genes, whereas RNA polymerase I transcribes rRNA genes, and RNA polymerase III transcribes rRNA, tRNA, and small nuclear RNA genes.
2. The primary transcript contains the coding region, exon, and the non-coding region, intron. hnRNA undergoes a process where the introns are removed and exons are joined to form mRNA by the process called splicing.
3. The hnRNA undergoes two additional processes called capping and tailing. In capping, an unusual nucleotide, methyl guanosine triphosphate, is added to the 5'-end of hnRNA. In tailing, adenylate residues (about 200-300) are added at the 3'-end in a template-independent manner.