Question

What happens to the mRNA during processing?

Answer 1

There are several steps in processing of mRNA

SPLICING

The mechnism by which introns or outrons are removed and exons are joined together to form a matured mRNA is RNA splicing.

5'CAP ADDITION

It is a modified guanine nucleotide that has been added to the front or 5' end of a eukaryotic mRNA shortly after the start of transcription.

The 5' cap cocnsists of 7-mrthylguanosine residue that is linked through a 5'-5'-triphhosphate bond to the first transcribed nucleotide. It is critical for recognition by the ribosomes and protection from RNases.

After start of transcription , the 5' end of mRNA is bound by a cap-synthesizing complex associated with RNA polymerase.. This complex catalyzes the chemical reaction that are required for mRNA capping.

EDITING

mRNA will be edited, changing the nucleotide composition of that mRNA.

This editing stops an early stop codon, which upon translation produces a shorter protien.

POLYADENYLATION

Polyadenylation is the covalent linkage of a polyadenyl moiety to a mRNA molecule.

after transcription has been terminated , the mRNA chain is cleaved through the action of a endonuclease complex associated with RNA poymerase . After mRNA has been cleaved around 250 adenosine residues are added to the free 3' end at the cleavage site.