AQA A Level Biology

Revision Notes

4.2.4 Eukaryotic Transcription

Eukaryotic Transcription

  • The genome within eukaryotic cells contains many non-coding sections
  • Non-coding DNA can be found:
    • Between genes, as non-coding multiple repeats
    • Within genes, as introns
  • During transcription, eukaryotic cells transcribe the whole gene (all introns and exons) to produce pre-mRNA molecules
    • pre-mRNA contains the introns and exons of a certain gene
  • Before the pre-mRNA exits the nucleus, splicing occurs:
    • The non-coding sections are removed
    • The coding sections are joined together
    • The resulting mRNA molecule carries only the coding sequences (exons) of the gene
    • mRNA contains only exons and exits the nucleus before joining a ribosome for translation

_Post-transcriptional modification of RNA, downloadable AS & A Level Biology revision notes

Image showing the splicing of pre-mRNA 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
  • This means that a single eukaryotic gene can code for more than one polypeptide chain
  • This is part of the reason why the proteome is much bigger than the genome

Alternative Splicing, downloadable AS & A Level Biology revision notes

Image showing the alternative splicing of a gene to produce two different proteins

Exam Tip

It is important you learn the terms pre-mRNA and mRNA, their location and whether they include introns as well as exons.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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