Answer to Question #163776 in Genetics for Safah

Question

When pre-mRNA is spliced and exons are then joined together, this happens randomly right? How can the chance be high enough then that the intentional mRNA is formed to then form the correct polypeptide sequence of the functional protein? Even if the chances are slim why does this not have an effect on organisms, some may argue this is a mutation in a way, as it is a change in nucleotide sequence.

Answer 1

When an RNA transcript is first made in a eukaryotic cell, it is considered a pre-mRNA and must be processed into a messenger RNA (mRNA). A 5' cap is added to the beginning of the RNA transcript, and a 3' poly-A tail is added to the end. In splicing, some sections of the RNA transcript (introns) are removed, and the remaining sections (exons) are stuck back together. Some genes can be alternatively spliced, leading to the production of different mature mRNA molecules from the same initial transcript.