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LS 3 Final > Lecture 14: Translation > Flashcards

Lecture 14: Translation Flashcards

1
Q

Prokaryotic translation: where is the first AA added, and by what?

A

Added to P site of ribosome by initiator tRNA

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2
Q

How does a ribosome know where to start translation on an mRNA?

A

mRNA has a Shine Dalgarno sequence, which base pairs with the 16S rRNA (small subunit)

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3
Q

What is the consensus Shine Dalgarno sequence?

A

AGGAGG

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4
Q

Specific subunits of prokaryotic ribosome (and what total ribosome is called)

A

50S and 30S associate to form a 70S ribosome

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5
Q

Length of 16S rRNA in small ribosome subunit?

A

1,540 nucleotides

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6
Q

What are Svedberg units?

A

Measurement of mass based on density gradient centrifugation

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7
Q

Composition of each ribosome subunit

A

Set of proteins complexed with one or more rRNAs

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8
Q

How can prokaryotic mRNA synthesize multiple polypeptides simultaneously and independently?

A

It has multiple Shine Dalgarno (ribosome-binding sites) - polycistronic genes

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9
Q

Where is the Shine Dalgarno sequence?

A

About 5-10 nucleotides upstream of start site

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10
Q

Sites of ribosome and their functions

A

E (holds exiting tRNA and binds to mRNA), P (holds tRNA with attached growing polypeptide), A (holds aminoacyl-tRNA)

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11
Q

Prokaryotic translation initiation: order of initiation factor binding

A

IF3, IF1, IF2

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12
Q

Prokaryotic translation: purpose of EF-Tu-GTP and how is it released?

A

Brings new aminoacyl-tRNA to A site; released through GTP hydrolysis

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13
Q

Prokaryotic translation: enzyme that catalyzes formation of peptide bond between 2 AAs

A

rRNA of 50S (large) subunit serves as the peptidyl transferase

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14
Q

Prokaryotic translation: what drives ribosome translocation step and how?

A

EF-G-GTP through GTP hydrolysis

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15
Q

Prokaryotic translation: what stop codons does RF1 recognize?

A

UAG, UAA

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16
Q

Prokaryotic translation: what stop codons does RF2 recognize?

A

UGA and UAA

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17
Q

Prokaryotic translation: what triggers termination?

A

Binding of RF1 or RF2 with RF3-GTP at A site: new polypeptide separated from tRNA, and GTP hydrolysis releases all subunits

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18
Q

Timing of transcription and translation in prokaryotes vs. eukaryotes

A

Simultaneous in prokaryotes; specially and temporally separated in eukaryotes

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19
Q

Subunits of eukaryotic ribosomes

A

Large (60S) and small (40S) subunits

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20
Q

Composition of eukaryotic 60S subunit

A

3 rRNAs and 49 proteins

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21
Q

Composition of eukaryotic 40S subunit

A

1 rRNA and 33 proteins

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22
Q

Where in the cell are eukaryotic ribosomes found?

A

Attached to membranes (like rough ER) or floating freely in the cytosol

23
Q

Difference between proteins synthesized in bound vs free ribosomes

A

Proteins in secretory pathway synthesized by bound ribosomes, proteins in non-secretory pathway synthesized by free ribosomes

24
Q

Fate of proteins synthesized by free ribosomes

A

Remain in cytosol, transported to nucleus, or incorporated into appropriate organelle

25
Q

Eukaryotic translation: where does first AA go and how does it get there?

A

Methionine brought to P site by initiator tRNA

26
Q

Eukaryotic translation: how is the amino end of the peptide blocked during initiation?

A

Acetylation

27
Q

Eukaryotic translation: how does a ribosome know where to start translation on an mRNA?

A

Small subunit and initiation factors recognize 5’ cap of mRNA

28
Q

Eukaryotic translation: what is the mRNA translation initiation sequence?

A

Kozak sequence: 7 nucleotides long, usually ACCAUGG (includes start codon)

29
Q

Eukaryotic translation: where is the Kozak sequence in mRNA found?

A

100 nt from 5’ cap

30
Q

Eukaryotic translation: purpose of eIF3 and eIF6

A

eIF3 binds to small subunit and eIF6 binds to large subunit to keep them disassociated

31
Q

Eukaryotic translation: components of ternary complex

A

eIF2-GTP and initiator tRNA (attached to Met)

32
Q

Eukaryotic translation: components of preinitiation complex

A

eIF1A, ternary complex (eIF2-GTP and initiator tRNA), eIF3-40S subunit

33
Q

Eukaryotic translation: how can cells block protein synthesis?

A

Phosphorylate a serine residue on eIF2 bound to GDP (to get GTP, GDP must be switched out and met-tRNAi must be bound, which cannot happen if phosphorylated)

34
Q

Eukaryotic translation: components of initiation complex

A

preinitiation complex and mRNA-eIF4E complex

35
Q

Eukaryotic translation: components of mRNA-eIF4E complex

A

CBC (cap-binding complex), eIF4E, eIF4G, eIF4A, eIF4B

36
Q

Eukaryotic translation: how do preinitiation complex and mRNA-eIF4E complex bind?

A

eIF4G and eIF3 interact with each other and stabilize binding

37
Q

Eukaryotic translation: function of initiation complex

A

Scan mRNA until it finds Kozak sequence with first AUG

38
Q

Eukaryotic translation: functions of eIF4A and eIF4B

A

eIF4A is helicase that unwinds RNA structures as initiation complex scans, and eIF4B activates eIF4A

39
Q

Eukaryotic translation: what happens when initiator tRNA recognizes Kozak sequence?

A

eIF2-GTP irreversibly hydrolyzes to eIF2-GDP, and eIFs dissociate

40
Q

Eukaryotic translation: function of eIF5

A

Brings in 60S-eIF6 (large subunit), then GTP hydrolysis on eIF5 releases rest of eIFs

41
Q

Eukaryotic translation: purpose of EF1alpha-GTP

A

Bring in new aminoacyl-tRNA at A site, then GTP hydrolysis releases it

42
Q

Eukaryotic translation: how is first peptide bond formation catalyzes?

A

Peptidyl transferase activity of large 60S subunit (rRNA)

43
Q

Eukaryotic translation: which parts of amino acids form peptide bond?

A

Carboxyl end of AA in P site with amino end of AA at A site

44
Q

Eukaryotic translation: what triggers translocation of ribosome?

A

Hydrolysis of EF2-GTP

45
Q

Eukaryotic translation: what happens once ribosome hits stop codon?

A

Entrance of release factors eRF1 (recognizes all stop codons) and eRF3-GTP at A site

46
Q

Eukaryotic translation: how is peptide separated from tRNA and subunits released?

A

GTP hydrolysis of eRF-GTP

47
Q

Translation rate for prokaryotes

A

20 AA per second

48
Q

Translation rate for eukaryotes

A

3-5 AA per second

49
Q

What is a polyribosome (polysome)?

A

Complex of mRNA and multiple ribosomes

50
Q

How are eukaryotic circular polysomes formed?

A

Poly(A) binding protein associates with eIF4G, allowing for efficient and rapid cycling of ribosomes

51
Q

What happens to mRNAs with premature stop codons?

A

Targeted for degradation through nonsense mediated decay (NMD)

52
Q

Purpose and location of exon-junction complexes (EJCs)

A

Bound 20-24 bp upstream of where two exons were joined by splicing, until displaced by ribosome during translation (if stop codon reached before final EJC), mRNA marked for degradation

53
Q

In prokaryotic translation, what is the first amino acid added?

A

N-formylmethionine or fMET

LS 3 Final (5 decks)

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