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LS 3 Midterm 3 > Translation > Flashcards

Translation Flashcards

1
Q

Prokaryotic Ribosome

A

70S (made up of 50S and 30S subunits)
50S subunit made up of 23S rRNA and 5S rRNA and proteins
30S subunit made up of 16S and proteins
EPA sites

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2
Q

Polysomes

A

in prokaryotes, several ribosomes can translate one mRNA simultaneously, even at the same time of transcription occurrence

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3
Q

Translation Initiation

A

mRNA and small subunit combine with initiator tRNA, which binds in the P site and base pairs with AUG (start codon)
large subunit binds and translation can begin

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4
Q

Initatiator tRNA

A

different from other methionyl-tRNAs

prokaryotes: formylated tRNA fMET
eukaryotes: special tRNA iMet

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5
Q

Shine Dalgarno Sequence

A

in prokaryotes
sequence preceding the start codon that tells the ribosome where to bind
binds to 16S rRNA of 30S subunit, near the E site
positions the mRNA correctly on the bacterial ribosome

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6
Q

Kozak Sequence

A

in eukaryotes
sequence enclosing the start codon in mRNA
that, with the 5’ cap, allows eukaryotic ribosomes to recognize and bind mRNA
highly conserved among organisms, the more conserved the higher the translation efficiency

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7
Q

Translation Initiation in Prokaryotes

A

IF3 binds to the 30S subunit in E site
IF1 binds to 30S subunit in A site
mRNA binds to 30S subunit, with Shine-Dalgarno sequence bound to 16S rRNA and AUG start codon positioned in the P site
fMet-tRNA binds to IF2, and then base pairs with the start codon

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8
Q

Initiation Factor 3 (IF3)

A

prevents association with 50S subunit and blocks the E site

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9
Q

Initiation Factor 1 (IF1)

A

blocks the A site of the 30S subunit

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10
Q

Initiation Factor 2 (IF2)

A

GTPase, binds to initiator tRNA with GTP attached
then helps position the initiation tRNA in the P site
hydrolyzes GTP if the correct base pair is achieved and 50S subunit attaches to begin initiation and have all three initiation factors dissociate (create the initiation complex)

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11
Q

Similarities in Mechanism of Translation Initiation Between Prokaryotes and Eukaryotes

A

initiation factors keep the ribosomal subunits separate, one helps the first tRNA to bind, which binds to start codon AUG
larger subunit binds when initiation factors unattach
GTP is hydrolyzed in both to cause initiation factors to unattach

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12
Q

Differences in Mechanism of Translation Initiation Between Prokaryotes and Eukaryotes

A

in EK, 5’ cap is bound to an IF, guides the mRNA to the small ribosomal subunit
Shine-Dalgarno sequence (PK) vs Kozak Sequence (EK)
eukaryotic translation can become circular to facilitate gene expression, polycistronic translation in prokaryotes
EK can have cap dependent or independent translation

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13
Q

Elongation

A

successive cycles of aminoacyl-tRNA binding and peptide bond formation occur until the ribosome reaches a stop codon

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14
Q

Elongation Overview

A

each tRNA must be activated (aminoacylated) by attaching the correct amino acid; uses ATP, done by aminoacyl transferase
correct aminoacyl tRNA binds in A site
peptide bond forms between aa on tRNA in P site and tRNA in A site (no ATP needed)
translocation: the tRNA in P moves to E site, and tRNA in A moves to P site

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15
Q

Aminoacyl tRNA Binding in A site in Elongation

A

binds to A site
facilitated by EF-Tu, which is a GTP-ase bound to the tRNA
only releases if they’re paired correctly

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16
Q

EF-Tu

A

GTPase that facilitates the aminoacyl tRNA binding into the A site
only releases the tRNA if the base pairs are correctly matched

17
Q

Peptide Bond Formation in Elongation

A

the proximity and positioning in large subunit catalyzes peptide bond formation
high energy bond from aminoacylation means no ATP required
N-terminus of A site attacks C-terminus of P site

18
Q

Hybrid State in Elongation

A

momentary, when amino acid chain is attached to the tRNA in the A site

19
Q

Translocation in Elongation

A

EF-G (a GTPase) binds to aminocyl tRNA in A site
GTP hydrolysis causes a conformational change, leading to ribosome translocation
causes tRNA in A to move to P, and that in P to move to E and exit

20
Q

Colinearity of Proteins and mRNA

A

5’-3’ polarity of mRNA corresponds to N-C polarity of protein

21
Q

Translation Termination

A

translation stops when a stop codon is encountered

mRNA and protein dissociate and ribosomal subunits are recycled

22
Q

Termination: Release of the Polypeptide

A

RF1 or RF2 recognize the stop codons and bind in the a site (instead of a tRNA)
peptide chain is transferred to the H2O instead of an amino acid, causing hydrolysis and release of aa chain
RF3 attaches to RF1/2, causing their release, then hydrolyzes GTP to release self

23
Q

Class I Release Factors

A

RF1 and RF2
recognize stop codons
shaped like tRNA

24
Q

Class II Release Factors

A

RF3

attaches to RF1/2 to dissociate it, then hydrolyzes GTP to dissociate itself

25
Q

Termination Ribosome Recycling

A

RRF binds to A site and mimics a tRNA
RRF recruits EF-G -GTP
EF-G-GTP catalyzes ribosome translocation, releasing the two remaining tRNA’s
IF3 helps dissociate the small and large subunits from mRNA, and begins the next cycle

26
Q

Ribosome Recycling Factor (RRF)

A

binds to A site and mimics a tRNA

recruits EF-G

27
Q

EF-G

A

binds to RRF in the A site, and catalyzes ribosome translocation using GTP hydrolysis in both elongation and termination

28
Q

RNA Mediation in Peptide Synthesis

A

RNA plays major role in protein synthesis
16s rRNA attracts mRNA through interactions
tRNA makes contact with 16s and 23s rRNA
peptidyl transfer reaction is catalyzed by 23s rRNA

29
Q

Ribosome Location

A

found on the rough ER and free in the cytoplasm

membrane bound ribosomes produce proteins that will be used in plasma membrane or secreted from the cell

30
Q

Cytosolic Ribosomes

A

produce proteins to be used in the cytosol

highly reducing environment inside the cell

31
Q

Signal Recognition Particle (SRP)

A

signal sequence at the beginning of the polypeptide tells the SRP to bind
the SRP then binds to the SRP receptor on the ER, causing the polypeptide to be directly synthesized into the ER

32
Q

Importin

A

binds to nuclear proteins (which are produced in the cytoplasm) at their nuclear localization sequence and transports into the nucleus
can move both mRNA and proteins

33
Q

Antibiotics

A

many antibiotics are specific to prokaryotic ribosomes, and abort translation prematurely

34
Q

5’ Cap Independent Translation

A

cap independent translation in eukaryotes requires extra proteins
internal ribosome entry site (IRES) made of 5’ UTR structural element

35
Q

RAN GTPase

A

binds to importin, which binds at nuclear localization sequence of proteins and transports them into the nucleus

LS 3 Midterm 3 (4 decks)

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