Question

Briefly outline the modifications that are made to the 5’ and 3’ ends of a primary transcript of one of your own genes.

Answer 1

In EUKARYOTES the nucleus contains atleast three RNA polymerases in addition to the RNA polymerase found in the organelles.

The RNA polymerase-1 transcribes rRNAs{28S,18S,5.8S}

The RNA polymerase-2 transcribes the heterogenous nuclear RNA(hnRNA)

The RNA polymerase-3 is responsible for trancription of tRNA,5srRNA,snRNAs

In the process of transcription at the 5 prime end and at 3 prime end of the gene there are some steps taking place.They are CAPPING,RNA SPLICING and POLYADENYLATION{TAILING} to form messenger RNA.

The complexity is that the primary transcripts of eukaryotes contain both EXONS and INTRONS and are non-functional.Therefore the gene is subjected to a process called SPLICING.

In the process of splicing the introns are removed and exons are joined in a defined order.

The hnRNA undergoes additional process called CAPPING and TAILING.

In capping- an unusual nucleotide METHYL GUANOSINE TRIPHOSPHATE is added at the 5 prime end of hnRNA

In tailing -adenylate residues are added at the 3 prime end of hnRNA ,now called as mRNA, which is transported to nucleus for TRANSLATION.