mRNA (9) Flashcards by M B

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

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What segments of the mRNA are located on the 5’ of the molecule?

cap of methylguanosine

UTR

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What segments of the mRNA are located on the 3’ of the molecule?

poly A tail

UTR

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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

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RNA splicing

removal of introns

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What does the mature cytoplasmic mRNA contain?

methylguanosine cap on the 5’ end

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What is the role of consensus sequences?

recruit machinery for splicing

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snRNPs

snRNAs + PROs

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spliceosome

complex of snRNA, hnRNA & PROs

formed as transcription occurs

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splice donor site is __’

5’

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splice acceptor site is ___ ‘

3’

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U PROs

recognize each other & bind to their substrates by base pairing at splice consensus site using their snRNAs

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what will effect binding of snRNP?

mutation of the intron

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what are the jobs of the spliceosome?

matching
cutting at junctions
ligation of hnRNA

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What is the role of U1 snRNA in intron splicing?

binds to the 5’ side, base pairs with snRNA

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What is the role of U2 snRNA in intron splicing?

binds to a certain region, the branch

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What is the role of U4/U6 & U5 snRNA in intron splicing?

bind displacing U1, spliceosome assembles

U4 will displace

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What is the role of U6 snRNA in intron splicing?

binds to U2 in the complex of 3 & cuts and ligates axons together

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What is the role of U5 snRNA in intron splicing?

holds 2 ends during cutting process

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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