Question

In a eukaryote, what modifications are made to mRNA before it is ready for export from the nucleus and subsequent translation?

Answer 1

Answer:

In Eukaryotes, mRNA undergoes following types of modification before being exported out of nucleus for translation.

Upon transcription before maturation, mRNA is called pre-mRNA. pre-mRNA goes through the following process to become matured mRNA.

1). Capping: Addition of 7-methylguanosine to the 5' terminus of the pre-mRNA. This helps mRNA to attach with ribosome during translation.

2). poly-A tail : Addition of 100-200 adenine molecules to the 3' terminus of the pre-mRNA. This helps to increase the stability of mRNA transcript and helps it to be exported out.

3). Splicing : Mechanism by which the introns are removed and exons are joined together. pre-mRNA has both introns(non-coding or junk sequences) and exon (coding sequence). In order to be exported out, introns should be removed. This is done by this process called splicing. (Alternative splicing, which exists in a few cases is a process which helps to make different mRNA transcripts from same pre-mRNA.)

Once all the above modifications are done, pre-mRNA is then matured into an mRNA and can be exported out of nucleus for translation.