RNA Processing in Eukaryotes
Biology: Cambridge International A Level, topic 6.2.3
RNA Processing in Eukaryotes
Before the information in eukaryotic mRNA is translated into protein, it is modified or edited in several ways
mRNA processing
- The initial mRNA molecule produced in eukaryotic transcription is known as "pre-mRNA" or the "primary transcript".
- The eukaryotic pre-mRNA undergoes extensive processing before it is ready to be translated.
- The additional steps involved in eukaryotic mRNA maturation create a molecule with a much longer half-life than a prokaryotic mRNA.
- Eukaryotic mRNAs last for several hours, whereas the typical E. coli mRNA lasts no more than five seconds.
Pre-mRNA splicing
- Eukaryotic genes are composed of exons and introns.
- Exons correspond to protein-coding sequences.
- Introns do not encode functional proteins. They may be involved in gene regulation but are removed from the pre-mRNA during processing.
- The process of removing introns and reconnecting exons is called splicing.
Pre-mRNA splicing - 2
- Splicing removes and degraded introns while the pre-mRNA is still in the nucleus.
- Splicing occurs by a sequence-specific mechanism that ensures introns will be removed and exons rejoined.
- The splicing of pre-mRNAs is conducted by complexes of proteins and RNA molecules called spliceosomes.
- Spliceosomes are composed of proteins and RNA molecules called snRNAs.
- Spliceosomes recognize sequences at the 5' and 3' end of the intron.
Alternative splicing
- Splicing can produce many different mRNA molecules from a single pre-mRNA molecule.
- This is because the pattern of exons and introns can be reordered during splicing.
- This is known as alternative splicing.
- Alternative splicing plays a role in gene regulation and increases the diversity of proteins that can be produced from a single gene.
Test yourself on RNA Processing in Eukaryotes
Which type of RNA is found in spliceosomes?