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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
Eukaryotic translation: where does first AA go and how does it get there?
Methionine brought to P site by initiator tRNA
26
Eukaryotic translation: how is the amino end of the peptide blocked during initiation?
Acetylation
27
Eukaryotic translation: how does a ribosome know where to start translation on an mRNA?
Small subunit and initiation factors recognize 5' cap of mRNA
28
Eukaryotic translation: what is the mRNA translation initiation sequence?
Kozak sequence: 7 nucleotides long, usually ACCAUGG (includes start codon)
29
Eukaryotic translation: where is the Kozak sequence in mRNA found?
100 nt from 5' cap
30
Eukaryotic translation: purpose of eIF3 and eIF6
eIF3 binds to small subunit and eIF6 binds to large subunit to keep them disassociated
31
Eukaryotic translation: components of ternary complex
eIF2-GTP and initiator tRNA (attached to Met)
32
Eukaryotic translation: components of preinitiation complex
eIF1A, ternary complex (eIF2-GTP and initiator tRNA), eIF3-40S subunit
33
Eukaryotic translation: how can cells block protein synthesis?
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
Eukaryotic translation: components of initiation complex
preinitiation complex and mRNA-eIF4E complex
35
Eukaryotic translation: components of mRNA-eIF4E complex
CBC (cap-binding complex), eIF4E, eIF4G, eIF4A, eIF4B
36
Eukaryotic translation: how do preinitiation complex and mRNA-eIF4E complex bind?
eIF4G and eIF3 interact with each other and stabilize binding
37
Eukaryotic translation: function of initiation complex
Scan mRNA until it finds Kozak sequence with first AUG
38
Eukaryotic translation: functions of eIF4A and eIF4B
eIF4A is helicase that unwinds RNA structures as initiation complex scans, and eIF4B activates eIF4A
39
Eukaryotic translation: what happens when initiator tRNA recognizes Kozak sequence?
eIF2-GTP irreversibly hydrolyzes to eIF2-GDP, and eIFs dissociate
40
Eukaryotic translation: function of eIF5
Brings in 60S-eIF6 (large subunit), then GTP hydrolysis on eIF5 releases rest of eIFs
41
Eukaryotic translation: purpose of EF1alpha-GTP
Bring in new aminoacyl-tRNA at A site, then GTP hydrolysis releases it
42
Eukaryotic translation: how is first peptide bond formation catalyzes?
Peptidyl transferase activity of large 60S subunit (rRNA)
43
Eukaryotic translation: which parts of amino acids form peptide bond?
Carboxyl end of AA in P site with amino end of AA at A site
44
Eukaryotic translation: what triggers translocation of ribosome?
Hydrolysis of EF2-GTP
45
Eukaryotic translation: what happens once ribosome hits stop codon?
Entrance of release factors eRF1 (recognizes all stop codons) and eRF3-GTP at A site
46
Eukaryotic translation: how is peptide separated from tRNA and subunits released?
GTP hydrolysis of eRF-GTP
47
Translation rate for prokaryotes
20 AA per second
48
Translation rate for eukaryotes
3-5 AA per second
49
What is a polyribosome (polysome)?
Complex of mRNA and multiple ribosomes
50
How are eukaryotic circular polysomes formed?
Poly(A) binding protein associates with eIF4G, allowing for efficient and rapid cycling of ribosomes
51
What happens to mRNAs with premature stop codons?
Targeted for degradation through nonsense mediated decay (NMD)
52
Purpose and location of exon-junction complexes (EJCs)
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
In prokaryotic translation, what is the first amino acid added?
N-formylmethionine or fMET

LS 3 Final (5 decks)

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