Post-transcriptional modifications - lecture 4 Flashcards
3 main preRNA modifications?
- 5’ capping
- RNA splicing
- 3’ Poly A tail
Where does post transcriptional modifications of the preRNA take place?
nucleus
How can the mRNA be degraded?
- 5’ cap removal
- shortening of poly(A) tail
- degradation of 5’ UTR coding sequence
Function of the poly(A) tail?
- proteins attach to the 3’ poly(A) tail interact with cap-binding proteins ..this enhances the binding of the ribosome to 5’ end of the mRNA
RNA splicing
introns tend to be removed
What is DNA -RNA collinearity?
proposes a strict correspondence between the RNA molecules transcribed and the proteins produced.
Seen in prokaryotes as they don’t have introns
How was non coding DNA discovered?
- mix DNA and complementary RNA together , heat to get ssDNA.
- when anneals DNA and RNA. , a loop of DNA is seen
What is alternative splicing?
one DNA sequence can lead to a large variety of proteins.
Sometimes you can remove whole exon s too
what happens to the tra gene in male flys, to determine its sex?
get upstream splice site, gets slightly longer transcript.
contains premature stop codon - makes non functional protein
What happens to the tra gene in female flys to determine sex?
Uses second splice site , Get functional Tra protein and therefore is female
What RNA types are found in both prokaryotes and eukaryotes?
- mRNA
- rRNA
- tRNA
What do micro and small RNAs do?
both prevent mRNAs from being translated into proteins
small interfering RNA mechanism
Double strand RNA spliced up by dicer protein.
To produce siRNA
Protein binds to siRNAs to form RISC .
RISC binds to mRNA and causes cleavage which causes degradation
MicroRNA mechanism
- double stranded region of RNA molecules are cleaved by Dicer to produce miRNA
- miRNAS combine with protein complex RISC and pair imperfectly with mRNA which leads to inhibition of translation
Alternate mechanism of microRNAS
Other miRNAs attach to complementary sequences in DNA and attract methylating enzymes, which methylate the DNA or histones and inhibit transcription
