In which cellular organelle do the three posttranscriptional modifications often seen in the maturation of mrna in eukaryotes occur?

Nucleus

Explanation:

Eukaryotic RNAs are synthesized in the form of precursors that will have to undergo a modification process in order to be functional. Prokaryotic mRNAs do not need to be modified after being synthesized and are linear with respect to the gene from which they were synthesized. That is, they are completely complementary. As for the prokaryotic rRNA and tRNA, the modifications they suffer are simple because they have to do with the cuts that the long precursor will suffer in which both species are included. However, eukaryotic mRNA, rRNA and tRNA, which are synthesized in the cell nucleus and nucleolus and subsequently used in the cytoplasm, need to undergo much more complex modification processes, not only to be functional but to be able to pass through the small nuclear pores to the cytoplasm. The objective of this conference is precisely to describe these post-transcriptional modification processes.

Modification at the 5 'or Cap 5' end

The 5 'end of the mRNA is modified in the eukaryotic nucleus (but not in the mitochondria or chloroplasts). Modification reactions are probably common in all eukaryotes. Transcription begins with a nucleoside triphosphate (almost always a purine, A or G). The first nucleotide retains its 5 'triphosphate group and forms the usual phosphodiester bond from its 3' position to the 5 'position of the next nucleotide.

Modification of the 3 'end or Poly Tail (A)

Most eukaryotic mRNAs have a polyadenyl acid sequence at the 3 'end. This terminal stretch of waste A is often described as Poly (A) tail and the mRNA with these characteristics is called poly (A) +. The poly (A) sequence is not encoded in the DNA, but is added to the RNA in the nucleus after transcription. The addition of poly (A) is catalyzed by the enzyme poly (A) polymerase, which adds ~ 200 residues of A to the free 3'-OH end of the mRNA.

Nuclear splicing

Splicing occurs in the nucleus, along with the other modifications that the newly synthesized RNA undergoes. The transcript obtains its cap at the 5 'end, loses its introns and is polyadenylated at the 3' end. Then the RNA is transported through the nuclear pores to the cytoplasm where it will be available for translation.