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cbg pant replication, transcription and translation > CBG Lecture 7: Translation > Flashcards

CBG Lecture 7: Translation Flashcards

1
Q

what is the ribosome

A

a massive ribonuceloprotein with ribozymal peptidyl transferase activity

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2
Q

what Svedberg unit are bacterial ribosomes

A

70S

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3
Q

what Svedberg unit are eukaryotic ribosomes

A

80S

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4
Q

where does translation occur

A

on the ribosomes

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5
Q

what does translation require

A

ribosome

charged tRNA, mRNA GTP and variety of initiation, elongation and termination factors to ensure accurate synthesis

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6
Q

what do ribosomes do

A

translate the codons of the mRNA into the sequence on a protein

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7
Q

how many subunits in a ribosome? what are they called

A

2 subunits
Large subunit
Small subunit

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8
Q

what does SSU do

A

small ribosomal subunit

binds mRNA, ensures codon pairs correctly with anticodon

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9
Q

what does LSU do

A

large ribosomal subunit
AS peptidyl transferase found here
where aas are attached to make a protein

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10
Q

what is the catalytic site of a ribosome made of?called?

A

peptidyl transferase active site
made entirely of rRNA
its a ribozyme

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11
Q

what is the error rate for translation of eukaryotes/bacteria

A

10-4 per aa

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12
Q

which translates faster, E.coli or humans?

A

E.coli by 10 times

E.coli : 20aa per sec

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13
Q

in prokaryotes and euks where does translation occur

A

in cytoplasm

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14
Q

WHAt machine is used for translation

A

ribosome, ribozyme, LSU, SSU

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15
Q

how is translation initiated

A

Initiation factors recruit tRNAi to the P site on the naked SSU, expending GTP

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16
Q

how many sites are on the SSU?

A

3
E(xit site)
P(eptidyl tRNA site)
A(minoacyl tRNA site)

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17
Q

what does the E stand for on the SSU

A

exit site

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18
Q

what does P stand for on SSU

A

peptidyl tRNA site

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19
Q

what does the A stand for on SSU

A

aminoacyl tRNA site

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20
Q

what is initiatior tRNA charged with in bacteria and endosymbionts

A

formylmethionine

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21
Q

what is initiator tRNA charged with in eukaryotes and archaea

A

methionine

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22
Q

whereabouts is the adenosine in tRNA

A

at 3’ end

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23
Q

how is initiator tRNAi removed? when is it removed

A

removed by peptidase after translation

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24
Q

outline initiation for translational initiation (inc. elF etc)

A

elF3 prevents LSU binding
elF1 blocks A site
elF2 brings tRNAi to P site
expends GTP, hydrolysis GTP, releases IFs allows LSU to bind

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25
Q

outline elFs and what they do in translational initiation

A

elF3- prevents LSU binding
elF1 - blocks A site
elF2 - brings tRNAi to P site, , hydrolysis GTP, releases IFs allows LSU to bind

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26
Q

what part of mRNA does the ribosome bind to first in eukaryotes

A

the methylguanosine 5’ cap, then finds the first AUG after that
the eukaryotic consensus (Kozac sequence) plays similar role to Shine-Dalgarno sequence but not as conserved

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27
Q

what does elF3 do

A

prevents LSU binding

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28
Q

what does elF1 do

A

blocks A(minoacyl tRNA) site

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29
Q

what does elF2 do

A

brings tRNAi to P(eptidyl tRNA) site, hydrolysis GTP, releases IFs allows LSU to bind

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30
Q

what is a Kozac sequence? what is it analogous to

A

eukaryotic consensus

similar role to SDS (Shine Dalgarno Seqeunce) but not as strongly conserved

31
Q

how is the AUG in prokaryotes distinguished from other AUGs

A

by a Shine Dalgarno Sequence

32
Q

why is AUG ambiguous in bacterial mRNA

A

because their mRNA is polycistronic, so AUG could be a start codon, inernal methionine or out of phase codon with reading frames

33
Q

why do eukaryotic mRNAs not need an SDS

A

because its monocistronic, ribosome just needs to bind mRNA 5’ cap then find the AUG after

34
Q

what is the chance of getting an SDS sequence in polycistronic mRNA

A

1/262144

35
Q

what is the chance of getting an AUG codon

A

1//64

36
Q

what provides evidence for LUCA

A

genetic code is almost universal
AUG is the typical start codon
there are only a small number of variations of genetic code

37
Q

how many GTPs are expended per aa in translational elongation
what is it used for

A

2GTP/aa - energy intensive

transfers the peptidyl on the P site tRNApeptidyl to the A site tRNAaminoacyl

38
Q

outline elongation factors and their roles used in translational elongation

A

EF1 brings charged tRNA to A site
EF2 shunts ribosome along
LSU catalyses peptide bond formation

39
Q

what does AUG code for in bacteria? in eukaryotes?

A

AUG - methionine in euks

formylmethionine in proks

40
Q

what can UGA also code for

A

selenocysteine instead of a stop

41
Q

how does ribosome distinguish between whether something is a stop codon or codes for an aa

A

based on secondary structures in mRNA

42
Q

how is the initiator aa removed from the mature protein

A

by a peptidase

43
Q

what does tRNA wobble lead to

A

non-Watson-Crick pairing at 3’ third base of codon

44
Q

how many aas? how many tRNAs

A

20 aas

40 tRNAs

45
Q

what are stop codons bound by

A

release factors (tRNA peptidyl hydrolase) terminating translation

46
Q

what does EF1 do

A

brings charged tRNA (eg. serine or threonine) to A site

47
Q

name some charged tRNAs

A

serine
threonine
(have OH group)

48
Q

what does EF2 do

A

shunts ribosome along - conformational change

uses GTP

49
Q

what part of ribosome catalyses peptide bond formation

A

LSU

50
Q

what does the LSU do

A

catalyses peptide bond formation

51
Q

what part of translational elongation requires ATP

A

2 ATP to attach aminoacyl to the tRNA in first place

for every amino acid added = 4 ATP

52
Q

how many GTPs and ATPs used during translational elongation

A

2GTP per AA

4ATP per AA

53
Q

how can mRNA convey meaning

A

through secondary structures
eg. convert stop to selenocysteine (UGA)
convert stop to pyrolysine (UAG)

54
Q

what does UGA

UAG code for

A

UGA - stop/selenocysteine

UAG - stop/pyrolysine

55
Q

how does mRNA convey meaning to ribosome about UGA/selenocysteine

A

converts STOP to selenocysteine by expending GTP

catalysed by a SEcIS : selenocysteine inserion element

56
Q

what is a polyribosome array

what does it do

A

lots of ribosomes

acts on a elF4-coiled mRNA to increase efficiency of translation

57
Q

how is protein folding detemined

A

by primary structure

58
Q

what is a molten globule

A

native secondary structure by liquid interior

59
Q

what is native state

A

the favoured entropic state but can get trapped in local energy minima

60
Q

give some examples of disease caused by faulty protein folding

A

CF
Marfan syndrome
Creutzfeld Jakob disease
Alzheimer’s disease

61
Q

how is CF caused

A

misfolding of transmembrane regulator

62
Q

how is Margan syndrome caused

A

misfolding of fibrillin

63
Q

how is Creutzfeldt Jakob disease caused

A

misfolding of prion protein due to extracellular aggregation

64
Q

how is Alzheimer’s disease caused

A

misfolding beta-amyloid due to extracellular aggregation

65
Q

what does a stacked beta sheet in a misfolding prion to

A

catalyses the misfolding of other prions leading to an exponential fatal misfolding catastrophe

66
Q

what are chaperonins

A

protein chaperones help fold proteins

67
Q

where does protein folding take place - is it an active process? how does it work

A

inside barrel of GroEL/GroES chaperonin - uses ATP

exposed hydrophobic residues on outside of protein are relocated to inside of protein

68
Q

what happens to unfoldable and unwanted proteins

A

theyre ubiquitinated and degraded in proteasomes

69
Q

what are proteasomes

A

they ubiquitinate and degrade unfoldable and unwanted proteins

70
Q

how do proteasomes ubiquitinate

A

attach a 5 ubiquitin tail to the waste protein

71
Q

how many subunits are present in proteasome

A

2
regulatory subunit: recognises 5Ubiquitinated protein, deubiquitinates and unfolds it
proteolytic subunit: degrades the protein

72
Q

what does the regulatory subunit of a proteasome do

A

recognises 5 U ubiquitinated protein, de-Us it then unfolds it

73
Q

what does the proteolytic subunit of a proteasome do

A

degrades the unwanted protein

cbg pant replication, transcription and translation (10 decks)

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