Post-transcriptional Modifications Flashcards
What is the precursor of mRNA ?
It is hnRNA ( heterogeneous nuclear RNA), which is produced by RNA polymerase II.
How are mature mRNA produced?
hnRNA ( is non-functional) undergoes post-transcriptional modification.
Name the three post-transcriptional modifications found in eukaryotes
- Splicing
- Capping
- Tailing
Name the two regions found on the structural gene.
- Introns (non-coding regions)
2. Exons (coding regions)
How is a mature mRNA formed?
By removing introns, through splicing & joining of the extrons.
How are introns removed from a pre mRNA?
A group of 5 snRNPs, or ribonucleoproteins , bind to the intron of the pre-mRNA & remove it, leaving only the exons.
How is a mature mRNA formed?
The 5 snRNPs bind to the intron and cause it to fold, bringing the 5’ & 3’ ends of the intron closer together, to form a loop.
The intron detaches & the splice sites connect to make a mature mRNA.
What happens to the SNRNPs after they detach from the intron?
They are used for more splicing.
Where does capping happen on a gene ?
On the 5’ end of the hnRNA.
The 5’ end of the hnRNA is capped by methyl guanosine triphosohate.
Where does tailing happen?
At the 3’ end of the hnRNA.
The 3’ end of the hnRNA undergoes tailing by addition of 200-300 adequate residues to form poly-A-tail.
What happens to the mature mRNA after post- transcriptional modification?
It is transported to the cytoplasm for protein synthesis.
What is the importance of post-transcriptional modifications?
It is the point where gene expression is regulated.
What is the function of the cap & tail on the mRNA?
- To facilitate the export of the mRNA from the nucleus
- To protect the mRNA from attack by cellular enzymes
- To help ribosome bind to the mRNA.
