post translational modification

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  • Created by: Sarah
  • Created on: 25-05-18 11:58
what do UTRs do?
1) sub cellular localisation 2) signals to regulate tranlation
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how do UTRs function in sub cellular localisation?
UTRs are recognised by proteins that have subcellular localisation and take the RNA there so it's translated in a specific place eg bicoid gives gradient
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what is an example of 3' + 5' UTRs regulating translation?
iron homeostasis
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which UTR is used for ferritin?
5' UTR
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which UTR is used for transferrin?
3' UTR
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when iron is low how does the UTR regulate it?
aconitase binds to ferritin 5' UTR + blocks translation. aconitase binds to 3' UTR of transferrin and prevents degradation
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what is the outcome of aconitase binding to them UTRs?
transferrin RNA made more stable + not degraded = more iron in thro transferrin. Aconitase binds ferritin and stops its translation- less iron stored
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how does aconitase stop working when iron levels are high?
iron binds aconitase causes conformational change so aconitase comes off ferrtin translated and tranferrin RNA degraded
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when cells are infected, quinsecent or have low food/energy how is global translation shut down?
by eIF2 + eIF2B
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what is eIF2B do?
guanine nucleotide exchange factor. recharges eIF2 by swapping GDP for GTP
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how does global translation shut down happen?
phosphorylating eIF-2 so eIF2B binds to eIF2 very tightly blocking its recylcling of GTP
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what is eIF2 notmal role?
eukaryotic initiation factor binds to met tRNA and small subunit to iniate ribosome asembly
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how can you increase degradation?
upregulating DAN which competes with eIF4F which does competitive binding for the cap. DAN binds to cap and chews away polyA tail
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how is RNA degradation controlled?
poly adenylation- make 200 adenosines when made but over time exonucleases cut down this like a timer. 30 adensoines then decapped and celaved up and degraded
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how can you make RNA last longer?
proteins in the cytoplasm can re-polyadenylate RNAs
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what allows more than one gene to be ptrsent on an mRNA?
IRES- internal ribosome entry sites
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how do IRES work?
they imitate the cap so that ribosomes can bind to them and initiate different reading frames. eiF4G (that binds small sub+met to scan) is required for IRES to bind + initiate translation. Can get ribosome independent of cap/polyA
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how do viruses use IREs cleverly?
use lots of IREs. To amplify the 2nd ORF they cleave eIF-4G so it can not interact with eIF4E but can still bind IREs
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when in humans are 2nd ORFs used a lot?
few genes but in apoptosis- done by cleaving eIF4G
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what do retroviruses need to prevent happening to their RNA genome?
it getting spliced
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how does a retrovirus get around the fact that you need splicing factors to recognise splice sites and escort out of nucleus when it doesn't splice RNA genome?
RNA-> DNA integrates in genome makes mRNA makes proteins = Rev. REV binds to the RNA genome + imitates splicing factors so it can get out
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how do you know if HIV has a high mobility?
high rev in blood
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what happens to B lymphocytes once they're matured?
at 1st are M bound to get feedback on antibody then become secreted antibodies when they've matured
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how does the M bound antibody B lymphocyte work?
the 1st stop codon is spliced out so has a TM domain. Splice site downstream of stop codon = stop codon II used. Stop codon I intron spliced out- has TM domain and polyadenylation much further down
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what happens to the secreted antibody?
goes to a short transcript as uses stop codon I- splice acceptor is lost and the first stop codon is not lost- cuts off the TM domain . Alters polyadenylation postiion is much further up
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what is it called when you can skip past AUG's?
leaky scanning
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how can you favour the first AUG?
have high levels of eIF-4F
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how does the proteins differ in leaky scanning?
all multiples of 3 so still same reading frame isoforms only differ by the sequnece of their N terminus
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what is the optimal sequence of nucleotides around the start site to help initiate translation?
kozak sequence
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what is an isoform?
different proteins from the same gene
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what is a really highly isoformed protein in drosophila?
Dscam- works in the NS. =has A, B, C, D groups and has 1 exon from each group gives over 38,000 isoforms
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what does alternative splicing do to the reading frame?
keeps the same ORF but gives differ3ent open reading frames to give different protiens
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3 ways to alternative splice?
1) alternative introns and extrons 2) mutually exclusive exons 3) internal splice site so cut through exon
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3 genes that control se determination in drosophila?
Sex lethal, transformer and doublesex
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which gene gives different isoforms to repress male/female specific genes?
doublesex
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which is the only functional protein in male drosophila?
doublesex- repressor of female genes
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why are sex lethal and transformer non functional in M drosophila?
they are spliced to give inactive proteins. 1) alternative exon inserted into leads to non functional sex lethal 2) transformer- alternative 3' splice site = non functional proteins
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how do you get the male isoform of doublesex?
remove exon -> gives repressor of F specific genes
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in Females how do you get the female doublesex isoform?
1) small amounts of sex lethal made by alternative promoter 2) sxl RNA binding binds to transformer blockes splice site get active transformer 3) transformer RNA binding binds to splice site to activate alternative splice site
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which one is the RNA binding protein in females that inhibits pslicing?
sex lethal
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which RNA binding protien in female Dros activates alternative splice site?
transformer
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how is the F isoform of doublesex different?
transformer activates splice site on dbsex- gives a different C terminus on the protein so represses M specific genes
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how does sex lethal block splicing of transofrmer?
binds to U2AF (splicesome protein) ito repress splicing
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how does sex lethal help itself?
small amount of sex lethal made by upstream genes alternative promoter then its RNA binding will bind to its own RNA so more functional sex lethal is made
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what does DAN compete with?
eIF4E for the cap
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Card 2

Front

how do UTRs function in sub cellular localisation?

Back

UTRs are recognised by proteins that have subcellular localisation and take the RNA there so it's translated in a specific place eg bicoid gives gradient

Card 3

Front

what is an example of 3' + 5' UTRs regulating translation?

Back

Preview of the front of card 3

Card 4

Front

which UTR is used for ferritin?

Back

Preview of the front of card 4

Card 5

Front

which UTR is used for transferrin?

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Preview of the front of card 5
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