mRNA (9) Flashcards
what are the segments of the mRNA?
- 5’ cap of methylguanosine
- a 5’ un-translated region (5’UTR)
a. Not converted into AA sequence - a continuous sequence of nucleotides encoding a PRO
- an untranslated region 3’ to the “coding” region (3’UTR)
- tail of about 250 A nucleotides –> polyAtail
What segments of the mRNA are located on the 5’ of the molecule?
cap of methylguanosine
UTR
What segments of the mRNA are located on the 3’ of the molecule?
poly A tail
UTR
Heterogenous nuclear RNA
hnRNA
heterogenous in size & sequence
located in the nucleus
Contains intervening non-coding regions, introns which are spliced out forming the smaller cytoplasmic form
RNA splicing
removal of introns
What does the mature cytoplasmic mRNA contain?
methylguanosine cap on the 5’ end
What is the role of consensus sequences?
recruit machinery for splicing
snRNPs
snRNAs + PROs
spliceosome
complex of snRNA, hnRNA & PROs
formed as transcription occurs
splice donor site is __’
5’
splice acceptor site is ___ ‘
3’
U PROs
recognize each other & bind to their substrates by base pairing at splice consensus site using their snRNAs
what will effect binding of snRNP?
mutation of the intron
what are the jobs of the spliceosome?
matching
cutting at junctions
ligation of hnRNA
What is the role of U1 snRNA in intron splicing?
binds to the 5’ side, base pairs with snRNA
What is the role of U2 snRNA in intron splicing?
binds to a certain region, the branch
What is the role of U4/U6 & U5 snRNA in intron splicing?
bind displacing U1, spliceosome assembles
U4 will displace
What is the role of U6 snRNA in intron splicing?
binds to U2 in the complex of 3 & cuts and ligates axons together
What is the role of U5 snRNA in intron splicing?
holds 2 ends during cutting process
how to is binding achieved in splicing
with base pairing
When does the spliceosome form?
when U4/U6 & U5 bind
ribozyme
RNA molecule with catalytic activity
apart of the intron
when does splicing only occur with an RNA molecule
some eukaryotes (protozoans)
mitochondria
chloroplasts
RNA can serve as both:
info storage &
catalysts
what is the role of the 5’ methylguanosine cap?
enables hnRNA of getting out of nucleus with protection from exonucleases
exporting attach to cap to transport out of the nucleus
start translation process
5’ methylguanosine cap structure
inverted guanine
after synthesis, guanine is added & then methylated
how do exonuclease attack?
outside inwards
how do exonucleases attack?
from the middle
mRNA processing
capping
splicing
tailing
what occurs in tailing of the mRNA?
endonuclease cuts in the middle, ~20 bp away from the polyA signal consensus sequence
As are added (without a template) by Poly(A)polymerase
what happens to remaining hnRNA after polyA tail is added?
RNA will get chopped up b/c the cap is gone
will begin to be fragmented by exonucleases
causes structure to loosen up & fall off to start again
What causes the polymerase to stop from forming mRNA from hnRNA?
will lose general transcription factors
what removes the polyA tail & where?
polyAribonuclease & in the cytoplasm
what determines the half-life of an mRNA? & when is it degraded? & what attacks it?
the length of the RNA tail
when ~30As remain, exonuclease
how does the polyA tail influence PRO expression? & what kind of control is it?
lifespan of mRNA influences the amount of PRO made –> translational level control
what influences the half life of mRNA?
length of polyA tail & 3’UTR
3’ UTR role
repetitive sequences that cause PROs to bind to them & protect them or recruit exnoculeases, influence the polyA tail
what stabilizes the mRNA?
3’ UTR sequence that prevents polyA ribonulease activity
what is important to the function of a PRO
the domain structure
what type of PRO means that their function can be altered by alternative splicing?
modular PRO structure
how does alternative splicing affect birds?
a single potassium ion channel in the ear can be altered many diff ways, each way changes the sensitivity to the potassium channel & changes the response to a diff pitch
what diseases can emerge from alternative splicing?
Progeria –> lamin A
Tau PRO –> alzheimer’s disease
Why is alternative splicing important in insects?
gender determination
the splicing out of the gene contain the stop contain producing a sex lethal PRO
males don’t do alternative splicing, females do
female has all of splice site PROs so she gets all of the exons, male doesn’t
how do splice enhancing PROs work?
some splice sites are weak & cannot attract U PROs to form spliceosomes (b/c they don’t match the consensus sequence very well) causing an exon to be omitted but splice enhancing PROs recognizes the intron & restores the splicing restoring the exon
what is normal alternative splicing?
enhancing PRO present
Enhancers
bind to weak splice sites & guide machinery
alternative splicing
splice enhancing PRO is missing, middle exon is skipped over
importance of introns
allow for a variety of PRO to be derived from one gene
