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Human Molecular B > Week 10 - Translation Pt I > Flashcards

Week 10 - Translation Pt I Flashcards

1
Q

elF4F is a heterotrimer consisting of what?

A

elF4G - scaffold protein eiF4E - binds the 5’ methyl cap elF4A - helicase that unwinds the 5’ structure elF4B binds 3’ poly (A)

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2
Q

What does mRNA bind to?

A

elF4G, elF3 and 40S subunit

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3
Q

What enables scanning?

A

elF1 and elF1A

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4
Q

What induces GTP hydrolysis by elF2?

A

elF5

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5
Q

What mediates joining or 60S subunit?

A

elF5B

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6
Q

What are the two stages of ending translation?

A

Termination reaction and post-termination reaction

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7
Q

RF1

A

Bacterial release factor that recognises UAA and UAG as signals to terminate the polypeptide translation

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8
Q

RF2

A

The bacterial release factor that recognises UAA and UGA as signals to terminate polypeptide translation

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9
Q

What is the ribosome recycling factor?

A

RRF

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10
Q

Where does protein synthesis occur?

A

Cytoplasm

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11
Q

What is mRNA?

A

Carries the genetic information

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12
Q

What is tRNA ?

A

Deciphers the codon

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13
Q

What is ribosomal RNA?

A

Associates with a set of proteins to form ribosomes

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14
Q

Why does tRNA contain non-standard bases?

A

Modification after transcription

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15
Q

What is the 3’ end of tRNA?

A

Amino acid attachment site Bind covalently Always CCA

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16
Q

What is anticodon?

A

Site of complimentary base pairing with mRNA unique for each species of tRNA

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17
Q

What does a combination of 4 bases give?

A

64 different codons for 20 amino acids

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18
Q

What does ribosome bind with?

A

A ribosome bind mRNA and tRNA

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19
Q

What are ribosomes?

A

Ribosomes are ribonucleoprotein particle comprising 2 subunits Each subunit contain a major rRNA(s) and a number of small proteins

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20
Q

In bacteria what does the 70S ribosomal subunits consist of?

A

Large: 50S (23S + 5S) Small: 30S (16S)

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21
Q

In eukaryotes what does the 80S ribosomal subunit consist of?

A

Large: 60S (28S + 5.8S + 5S) Small: 40S (18S)

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22
Q

How many binding sites do ribosomes have?

A

The ribosome has 3 tRNA-bonding sites. A, P and E

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23
Q

What occurs in A site?

A

An aminoacyl-TRNA enter the A site

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24
Q

What occurs in P site?

A

Peptidyl-tRNA ( a tRNA carrying the nascent polypeptide chain) is bound to P site

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25
Q

What occurs in E site?

A

Deacylated TRNA (lacking any amino acid) exit via E site

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26
Q

I’m brief, what is the first stage of translation?

A

Before peptide formation, peptide tRNA occupies the P site, and aminoacy-tRNA occupies A site

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27
Q

In brief, what is 2nd stage of translation?

A

Peptide bond formation. Polypeptide is transferred from peptide is tRNA in P site to aminoacyl-tRNA I’m A site

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28
Q

In brief, what is the 3rd stage of translation?

A

Translocation moves ribosome one codon, places peptidyl tRNA in P site, deacylated tRNA leave via E site and A site is emptied for the next AA-tRNA

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29
Q

What is accuracy of translation controlled by?

A

Specific mechanisms at each stage. Error rates differ at each stage of gene expression

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30
Q

Give examples of some errors that may occur in translation?

A

Wrong base frameshift Wrong tRNA Wrong AA Wrong aminoacyl-tRNA

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31
Q

What does bacteria need to start initiation?

A

30 subunits and accessory factors (initiation factors)

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32
Q

what is the ribosome-binding site

A

A sequence on bacterial mRNA that includes an initiation codon that is bound by a 30S subunit in the initiation phase of polypeptide translation

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33
Q

Is initiation of translation a function of intact ribosomes?

A

No it is undertaken by the separate subunits, which reassociate during the initiation reaction

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34
Q

When does recognition of mRNA occur ?

A

Small subunit bond to form an initiation complex at ribosome binding site

35
Q

In bacteria, what does initiation of translation require ?

A

Initiation of translation require separate 30S and 50S subunits

36
Q

What initiation factor are needed in bacterial initiation?

A

Initiation factors (IF-1, IF-3 and IF-3) which bind to 30S subunit, are also required

37
Q

What is the function of IF-3?

A

Stabilises the free 30S subunits Inhibit premature binding of 50S subunit It enable 30S subunit to bind initiation site Check the accuracy of recognition of the first amino acids-tRNA

38
Q

What is the function of IF-2?

A

Bind a special initiator tRNA and controls its entry into the ribosome

39
Q

What is the function of IF-1?

A

Binds in the vicinity of A site Prevents aminoacyl-tRNA from entering

40
Q

Before 50s subunit joins, what must occur first?

A

A 30S subunit carrying initiation factors Bind to an initiation site on mRNA to form an initiation complex

41
Q

What must occur in order for 50s subunit to join the 30s subunit?

A

IF-3 must be released to allow 50S subunit to join the 30S-mRNA complex

42
Q

What is the initiation site on bacterial mRNA ?

A

An initiation site on bacterial mRNA consist of AUG initiation codon

43
Q

What precedes 10 bases before it?

A

Shine-Dalgarno polypurine hexamer

44
Q

What is shine-dalgarno sequence ?

A

Polypurine sequence is AGGAGG centred about 10bp before the AUG initiation codon on bacterial mRNA

45
Q

What is complementary to Shine-Dalgarno sequence?

A

Complementary to the sequence at 3’end of 16S rRNA during initiation

46
Q

Translation starts by what A.A?

A

Translation starts with a methionine amino acid usually coded by AUG

47
Q

T or F: the same methionine tRNAs are involved in initiation and elongation

A

False: different methionine tRNAs are involved in initiation and elongation

48
Q

What is N-formal-methionyl-tRNA (tRNAfmet) ?

A

The aminoacyl-tRNA that initiates bacterial polypeptide translation The amino group of methionine is formylated

49
Q

What is tRNAmMet?

A

The bacterial tRNA that inserts methionine at internal AUG codons

50
Q

What are the unique features of initiator tRNA?

A

NH2 group of methionine - formylated. Bases at the last position of stem are unpaired 3 G-C base pairs are required to allow tRNAfMet to be inserted directly into P site

51
Q

What tRNA enters the 30S?

A

Only tRNAfMet enters partial P site on 30S subunit bound to mRNA

52
Q

What tRNAs enter the 70S?

A

Only as-tRNA enter A site on complete 70S ribosome

53
Q

What occurs first in initiation process in bacteria?

A

IF-1 and IF-2 bind the 30S

54
Q

What occurs 2nd In the initiation process in bacteria?

A

IF-2-GTP bind the initiator fMet-tRNAf. This allows it to enter the partial P sure in the 30S subunit

55
Q

What occurs last in the initiation process in bacteria?

A

IF-3 leaves and 50s subunits join

56
Q

What occurs first in initiation in Eukaryotes ?

A

Eukaryotic 40S ribosomal subunit bind to the 5’ end of mRNA (methylated cap)

57
Q

What occurs 2nd in initiation in eukaryotes?

A

40s scan mRNA and migrates to initiation site (AUG) + Kozak sequence

58
Q

What is the initiation site in eukaryotes?

A

A eukaryotic initiation site consists of a ten-nucleotide sequence that include an AUG codon (Kozak sequence)

59
Q

What occurs last in the initiation process in eukaryotes?

A

60S ribosomal subunit join the complex at initation site

60
Q

what happens if leader is long?

A

subunits May form queue

61
Q

What is IRES ?

A

A eukaryotic messenger bra sequence that allows a ribosome to initiate polypeptide translation without migrating from 5’end

62
Q

How many IF in eukaryotes?

A

At least 12

63
Q

1st stage of initation pathway in eukaryotes

A

Ternary complex formation elF2 bind the initiator Met-tRNAi and GTP forming ternary complex that binds to the 40S subunit before it associates with mRNA

64
Q

2nd stage of initiation pathway in euk.

A

43S preinitation complex formation 40S subunits assisted by elF1A, elF1 and elF3 interact with complex elF5 bind to 30S subunit elF1, elF3 and elF5 and ternary complex might interact to form multi factor complex that bind to 40S subunit as single entity

65
Q

3rd stage of initiation pathway in euk.

A

mRNA activation Eukaryotic mRNA passes the nuclear pre into the cytoplasm as a structure molecule coated with polypeptides mRNA is activated by removing secondary structures and proteins from 5’ end before translation Cap binding process f

66
Q

4th stage

A

mRNA entry into preinitiation complex elF4G subunit interact with elF3. Recruit 5’end of mRNA to 43S preinitiation complex Structural changes take place when elF1A and elF1 bind to 40S subunit

67
Q

5th stage

A

5’-3’ scanning to detect the initiation codon 43S complex moves along mRNA in a 5’-3’ direction ATP dependent movement continues until the AUg initiation codon on mRNA is aligned with anti-codon in the initatior tRNA elF1 and elF1A both contribute to search for initiation codon

68
Q

6th stage

A

Initiation codon recognition Hydrolysis of elF2- bound GTP and Pi release elF5 stimulates elF2 to convert bound GTP to GDP and PI elF1 which usually prevents pi escape is displaced from P site when met-tRNAi bind to AUG.
Escape of Pi triggers conformational change Convert open mRNA entry channel into a closed channel 48S IC can join 60S subunit

69
Q

7th stage

A

60S subunit joining and IF displacement elF5B.GTP facilitates the joining of 60s subunit to the 48S preinitiation complex elF1, elF2.GDP, elF5 are elevated during joining

70
Q

8th stage

A

Hydrolysis of elF5B-bound GTP and release of elF5B and elF1A elF1A and elF5B.GDP are released after GTP bound is hydrolysed release of elF1A from 80S complex frees the A site to participate in elongation process

71
Q

What is elF2 ?

A

GTPasee

72
Q

What is elF2B?

A

Exchange factor

73
Q

What does elF2 consist of?

A

alpha and beta subunits

74
Q

What does elF4b?

A

Stimulates elF4a helicase

75
Q

What does PAPB do?

A

Binds 3’ poly (A)

76
Q

What does elF1 and elF1A enable?

A

Scanning

77
Q

What does elF5 induce?

A

GTP hydrolysis by elF2

78
Q

What does elF5b mediate?

A

Joining of 60S subunit

79
Q

What elFs are involved in pre-initiation complex?

A

elF2, elF3, elF1 and elF1A

80
Q

What elFs are involved in cap-binding?

A

ElF4A, B, E and G

81
Q

What elFs are I cocked in 48S complex ?

A

elF2, elF3, elF1 and 1A, elF4A+B+F

82
Q

What is elF4F?

A

Heterotrimer consisting of; eif4g (scaffold proteins) eif4e (binds the 5’ methyl cap) eif4a (a helicase that unwinds the 5’ structure)

83
Q

What is EF-Tu?

A

Monomeric G protein whose active form binds to amino acid tRNA

84
Q

What is EF-T?

A

Guaninine nucleotide exchange factor Required to mediate the replacement of GDP by GTP

Human Molecular B (13 decks)

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