Post-Transcriptional Changes to mRNA (Edexcel International A Level Biology)

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Biology & Environmental Systems and Societies

One Gene Can Code for More Than One Protein

  • Gene expression can be regulated after an mRNA transcript has been produced
  • In eukaryotes, transcription and translation occur in separate parts of the cell, allowing for significant post-transcriptional modification to occur
  • Post-transcriptional modification mechanisms include
    • Splicing
    • Alternative splicing


  • Polypeptides are made during the process of protein synthesis, during which the DNA base code is transcribed and translated
  • The DNA code within eukaryotic cells contains many non-coding sections
  • Non-coding DNA can be found within genes; these sections are called introns, whilst sections of coding DNA are called exons
  • During transcription, eukaryotic cells transcribe both introns and exons to produce pre-mRNA molecules
  • Before the pre-mRNA exits the nucleus, a process called splicing occurs
    • The non-coding intron sections are removed
    • The coding exon sections are joined together
    • The resulting mRNA molecule contains only the coding sequences of the gene
  • Since these modifications are made after transcription occurred, they are called post-transcriptional modifications

Splicing of pre-mRNA 1Splicing of pre-mRNA 2

Pre-mRNA is spliced before it exits the nucleus

Alternative splicing

  • The exons (coding regions) of genes can be spliced in many different ways to produce different mature mRNA molecules through alternative splicing
  • A particular exon may or may not be incorporated into the final mature mRNA
  • Polypeptides translated from alternatively spliced mRNAs may differ in their amino acid sequence, structure and function
  • This means that a single eukaryotic gene can code for multiple proteins
  • This is part of the reason why the proteome is much bigger than the genome

Alternative Splicing

Alternative splicing of a gene can produce more than one type of protein

Exam Tip

It is important you learn the terms pre-mRNA and mRNA, their location and whether they include introns as well as exons. A handy way to distinguish between introns and exons is to remember that EXons are EXpressed.

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

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