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
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
Image showing the alternative splicing of a gene to produce two different proteins
Examiner Tip
It is important you learn the terms pre-mRNA and mRNA, their location and whether they include introns as well as exons.
