mRNA processing Flashcards
General information about mRNA processing
Nucleus
preRNA processed to form mature mRNA
promotor start of 5’ end
information for mRNA is discontinuous in DNA
Exons joined in order they are in DNA to form a functional gene
introns are removed
what is the splice donor site
where the splicosome binds at the beginning of an intron
motif that cell looks for
AGGU
5’ end
what is the spliceosome
snRNP and pre- mRNA complex
Explain the addition of the polyA tail
polyadenylation added to 3' end one base at a time 11-30 bases down from AAUAAA prevent degredation in cytoplasm get shorter - regulate translation
Explain the addition of the cap
modified guanine nucleotide
Added to 5’ end - phosphodiester
hydrolysis terminal phosphate mRNA
reacts with a-phosphate of GTP - 5’-5’ phosphate linkage
Cap methylated N7 position purine ring - 7-methylguanylate cap
help bind to small subunit (40s) of the ribosome
prevent degradation in the cytoplasm
explain bacterial transcription
All coding information for 1 protein is in 1 block
once transcribed the mRNA is used straight away in the same place
Only 1 RNA pol
Sigma factors - bring RNA pol to different sections of genes
promotor is ‘pribnow box’ TATAAA
This is different to eukaryotes - target for AB
The other name for pre-RNA
Heterogenous nuclear RNA (hnRNA)
Sequence of events in RNA processing
introns start with GU and end with AG
uses small ribonuclear proteins - snRNPs
U1 bind AGGU (splice donor site)
U2, U4, U5 (splice acceptor CAG), U6 binding - complete spliceosome (protein and preRNA)
cleavage of splice donor sequence AG GU - phosphodiester bond broken
Tries to fold
A residue in intron - branchpoint
GU bind to A - phosphodiester 5’ phosphate G, 2’ OH A
Phosphodiester at end intron cleaved
lariat structure - recognised as waste and broken down
adjacent exons ligated
what is the splice acceptor site
bases end of intron Pry15NCAG CAG - highly conserved U5 bind 3' end
what is a mutation
heritable change in sequence of gene
proportion of mutations in human disease in splice donor/acceptor
33%
what is thalassemia
inherited disorder
imbalance in amount of globulin chains (a and B) in Hb
complications as a result of thalassemia
severe anaemia - 12 months extramedullary haematopoiesis hepatomegaly/hepatospenomegaly - attempt to produce more RBC iron overload - excessive absorbtion of iron due to anaemia hepatic fibrosis and cirrhosis skin darkening cardiomyopathy endocrinopathies skull attempt to make RBC
distribution of thalassemia
more people on silk road - trade
what is the cause of B thalassemia
deficiency in B chains
