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Block 1 Week 1 > Protein Translation & Modification > Flashcards

Protein Translation & Modification Flashcards

1
Q

Where does trxn occur? Where does translation occur?

A

trxn= nucleus; translation= cytosol

-means the mRNA strand has to relocate

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2
Q

How does mRNA get into cytosol to be translated?

A
  • via nuclear pore complex
  • must be packaged in a specific manner, if incorrectly packaged will not be recognized by nuclear pore & won’t be able to move into cytosol
    • movement of mRNA into cytosol IS A RATE LIMITING STEP
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3
Q

What are eukaryotic ribosomes? Where made? What is their role?

A
  • individual subunits, 60s=large, 40s= small, together get 80s
  • produced & assembled in nucleus, exported as separate subunits to cytosol
  • factory responsible for translation
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4
Q

Roles of the ribosomal subunits?

A
  • 40s (small) locates & bind mRNA, oversees tRNA binding to codons
  • 60s (large) catalyzes peptide bond formation
  • 80s (both) assembles upon initation of translation
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5
Q

what does “s” stand for in 80s vs 60s ribosomal subunits?

A

sedimentation coefficient

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6
Q

Prokaryotic ribosome structure?

A

Large (50s) subunit

small (30s) subunit

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7
Q

80s ribosomal structure during translation?

A
  • three tRNA binding sites, one mRNA binding sites.
  • right to left*
    1) A: amino-acetyl-tRNA site binds incoming tRNA
    2) P: peptide site: growing polypeptide chaine is attached
    3) E: exit site where empty tRNA is released
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8
Q

4 steps of protein translation?

A

1) Preinitiation
2) Initiation
3) Elongation
4) Termination

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9
Q

What is the pre-initiation step in translation?

A

1) binding of methionine-tRNA & mRNA to 40s subunit

forms the pre-INITATION COMPLEX

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10
Q

What is the initiation step in protein translation?

A

1) binding of 60s subunits to pre-initation complex

2) scanning, recognizing initiating start codon AUG

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11
Q

What is the elongation step in translation?

A

1) new tRNA enters (decoding)
2) peptide bond forms (transpeptidation)
3) ribosomal subunit resets (translocation)

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12
Q

What is the termination step in translation?

A

1) stop codon recognition
2) ribosomal dislocation
3) terminal transferase activity c-terminal COOH

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13
Q

What are initiation & elongation factors?

A
  • proteins that have roles in translation but aren’t associated w/ ribosome
  • oncogenes & tumor supressor genes modify these factors to affect protein synthesis
  • drugs can inhibit their acitivy to block translation
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14
Q

1) Initation factors role?

2) Elongation factors role?

A

1) involved in pre-initation/initation phase

2) assit in ribosomal peptide bond formation, translocation of mRNA, resetting ribosomes

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15
Q

eIF2A?

eIF2b?

A
  • eukaryotic initiation factor *
    1) drives MET-tRNA binding to 40s subunit via GDP–>GTP
    2) exchanges eIF2A’s GDP–>GTP

makes pre-initation complex

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16
Q

Rate limiting step in the production of pre-initation complex?

A

binding of 5’CAP of the mRNA by initation factors which then help the mRNA find the preinitation complex
-because requires GTPase activity & IF/stabilization factors

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17
Q

What specifically happens during initation phase?

A

1) eIF4A unwinds mRNA, helps MET-tRNA find start codon
2) eIF5B helps large subunit bind, accelerates GTPase activity of 2A
3) GTP hydrolysis allows eIF2A to dissociate

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18
Q

Decoding step of elongation?

A
  • new incoming tRNA sits in the A site catalyzed by EF1A

- GTP hydrolyzed when tRNA/codon pairing occurs

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19
Q

GTP hydrolysis mean?

A

GTP–>GDP via a GTPase

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20
Q

Transpeptidation step of elongation?

A

1) bond breaks between P-site tRNA and it’s polypeptide chain
2) new peptide bond formed w/ A-site tRNA
- catalyzed by 60s
3) rxt shifts 60s, moving tRNAs to E & P sites

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21
Q

Translocation step in elongation?

A

1) mRNA moves up 3 nucleotides
2) 40s resets w/ the already moved 60s to prepare new cycle
3) catalyzed by GTP bound Ef2
4) tRNA in E sites dissociates

22
Q

What is the chain of termination?

A

1) termination
- stop codon reached
- no tRNA recognize termination codon, A site left open
2) release
- release factors bind A site
- peptidyltransferase ran hydrolyzes COOH end of polypeptide
- new protein released
3) disassembly
- mRNA, 40s, 60s dissociate
- requires GTP and RF’s (release factors)

23
Q

What happens if pre-initiation, initiation, elongation & termination don’t happen correctly?

A
  • if any part of process is completely blocked = DEATH

- if not completely blocked…just altered can result in increased/decrased translation

24
Q

What are the most common errors in translation?

A
  • synthesis of erroneous proteins (wrong aa added)
  • premature abandonment of translation
  • due to errors by the ribosomes
25
What affects the rate of translation?
-the regulation of the accessory proteins | initiation & elongation factors
26
How do signals altering eIFs lead to cancer?
- many growth factors cause phosphorylation of IFs, increasing their affinity for 5'cap, & increasing transaltion - some tumor suppressors are phosphatases that dephosphorylate eIF & decrease translation, therefore decreases the amount of tumor suppressors
27
How control increasing or decreasing translation in regards to eIF-4E?
- phosphorylation by binding proteins INCREASES translation | - dephosphorylation DECREASES translation
28
Where do proteins destined for Plasma membrane & specific organelles go for processing?
- the proteins contain a signal sequence that targets the ER - sorting sequences define end location - additional proteins recognize the sequence & help w/ targeting
29
Importance of protein folding?
- need to be properly folded into functional structures | - proper folding is essential for proper modification, targeting & function
30
What are post-translational modifications? What determines which ones to apply to a protein?
- involve any change in the overall chemical nature of the protein after translation - used to direct protein to it's final destination - based on specific cell type's needs, environment, and interacting molecules
31
Why need post translation modifications?
- so that proteins can perform specific functions & go to correct final desitnation - increases diversity & functionality of all proteins in cell (proteome)
32
Most of the modifications produced in the ER?
-are constitutive & remain until protein is degraded
33
Types of protein modifications?
-phosphoryaltion,N-linked glycosylation, disulfide bonds, lipidation, sulfating, ubiquitation, sumoylation
34
What is phosphorylation?
- a PTM - reversible addition of a phosphate (PO4) group - on serine, threonine, tyrosine - promotes -activation/deactiviation of enzymes/receptors via conformational changes - dynamic & regulated, involved in signal transduction
35
kinase vs phosphatase?
- kinase: adds phosphate group | - phosphatase: removes phosphate group
36
What is N-linked Glycosylation? Where occur?
- only in Eukaryotes - covalent addition of sugars/carbs to ASN reside of protein - occurs in ER at an Asn-X-Ser/Thr consensus sequence - is a quality control mechanism
37
How N-linked glycosylation occur?
- occurs COTRANSLATIONALLY - catalyzed by glycosyl transferases - initial sugar added as one preformed unit
38
Why do we have glycosylation?
Essential for function of some proteins: 1) protects from proteases 2) can facilitate proper folding 3) can participate I cell adhesion/ligand recognition 4) regulated glycosylation can alter protein function
39
disulfide bond formation
- occurs in ER (oxidative env) - formed between 2 cysteine - sometimes required for protein folding, may require glycosylation to fold properly - formed/broken by PDI
40
what is protein disulphide isomerase? relationship to disease?
- catalyzes formation & breakage of disulfide bonds - via oxidation of cysteine - checks for & corrects incorrect cys-cys bridges - in the ER
41
Where disulfide bonds occur?
- oxidative env - never in cytosol - extracellualr faces of transmembrane proteins
42
PDI & neurodegeneration
- over production of free radicals inhibit PDI - decreased levels of PDI result in increased protein misfolding - been linked to neurodegenerative diseases
43
cytosolic lipid modification? (3)
- faciliatie membrane & protein-protein interactions 1) myristoylation 2) palmitoylation 3) prenylation
44
myristoylation
irreversible addition of myristic acid moiety to N terminus | -in signaling proteins
45
palmitoylation
reversible addition of palmitate to sulfate of internal cys residues -cytosol & er
46
prenylation
-reversible addition of farnesyl or geranyl groups to C-term cysteines
47
Where/how/what is sulfating?
- PTM - occurs in trans-golgi - important for many extraceluuar metric protein & mucous
48
Ubiquitination, what does it do?
- addition of ubiquitin protein to lys of target proteins - targets protein for degradation - involved in cell cycle regulation, DNA repair & protein trafficking
49
What is sumoylation?
- reversible addition of SUMO to target proteins, affect protein function - regulates nuclear-cytosol transport, cell cycle, protein stability & localization - deSUMOylating enzymes reverse modification
50
What are the consequences of sumoylation?
- mutations in SUMOylation enzymes or protein targets leads to incorrect protein trafficking - associated w/ neurodegenerative disorders

Block 1 Week 1 (9 decks)

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