Messenger RNA

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•  Eukaryotic cells modify mRNA after transcription

In eukaryotes, there are three post-transcriptional events that must occur in order to form mature messenger RNA:


  • Capping involves the addition of a methyl group to the 5’-end of the transcribed RNA
  • The methylated cap provides protection against degradation by exonucleases
  • It also allows the transcript to be recognised by the cell’s translational machinery (e.g. nuclear export proteins and ribosome)


  • Polyadenylation describes the addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
  • The poly-A tail improves the stability of the RNA transcript and facilitates its export from the nucleus


  • Within eukaryotic genes are non-coding sequences called introns, which must be removed prior to forming mature mRNA
  • The coding regions are called exons and these are fused together when introns are removed to form a continuous sequence
  • Introns are intruding sequences whereas exons are expressing sequences
  • The process by which introns are removed is called splicing

Post-Transcriptional Modifications

post transcription

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•  Splicing of mRNA increases the number of different proteins an organism can produce

Splicing can also result in the removal of exons – a process known as alternative splicing

The selective removal of specific exons will result in the formation of different polypeptides from a single gene sequence

  • For example, a particular protein may be membrane-bound or cytosolic depending on the presence of an anchoring motif

Alternative Splicing

alternative splicing