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20 Cards in this Set

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Where's the anticodon?
a. up there
b. down there
c. over here
d. all of the above
b. down there
Hee Hee
In prokaryotic translation, what are the required initiation factors?
IF1, IF2 (GTP), and IF3
What are the three steps in the formation of the initiation complex in prokaryotes?
Step 1:
-IF3 binds to 30S subunit
-IF1 is placed at A-site in the 30S subunit
-The AUG codon of the mRNA aligns at the P-site
Step 2:
-IF-2 (GTP-bound) binds to 30S
-The anticodon of fMet-tRNA^fMet pairs with the first codon (AUG) in the mRNA
Step 3:
-The 30S and 50S subunits merge under hydrolysis of GTP.
-IF1, IF2, and IF3 are released, changing the structure of the subunits
What are ancillary protein factors required for elongation in prokaryotic translation?
EF-Tu (GTP), EF-Ts, and EF-G (GTP)
What does EF-Tu (GTP) do during prokaryotic translation?
It brings the activated tRNA to the A-site during elongation.
What does EF-G (GTP) do during prokaryotic translation?
It facilitates translocation by binding to the ribosome, ejecting the tRNA, and shifting the mRNA by one codon.
What is the significance of IF-3 binding to the 30S subunit in translation initiation?
It prevents the 30S subunit from associating with the 50S subunit too soon.
What is the significance of IF-1 binding to the A-site in the 30S subunit in translation initiation?
It prevents tRNA from binding too soon.
How does EF-Ts help activate EF-Tu in prokaryotic translation?
EF-Tu binds to GDP when it is inactive. EF-Ts binds to the EF-Tu-GDP complex and activates EF-Tu by facilitating the dissociation of GDP. This allows EF-Tu to bind to GTP instead.
Why does EF-Tu bind to GTP instead of GDP after EF-Ts facilitates GDP dissociation in prokaryotic translation initiation?
Because GTP is generally found in higher concentrations in the cell, predisposing EF-Tu to bind to GTP instead of GDP.
What happens to GTP after EF-Tu binds to the A-site of the ribosome in prokaryotic translation?
It is hydrolyzed to GDP, then GDP dissociates, causing a conformational change in EF-Tu.
What are the steps in prokaryotic translocation?
1. EF-G-GTP binds to the ribosome in the vicinity of the A-site.
2. EF-G-GTP binding pushes the tRNA with the growing polypeptide chain from the A-site to the P-site, and the uncharged tRNA in the P-site is shifted to the E-site.
3. Interaction with the ribosome (which functions as GAP - GTPase activating protein) causes EF-G to hydrolyze its bound GTP to GDP + Pi.
4. EF-G-GDP dissociates from the ribosome.
tRNAs are linked to the mRNA by _______________ base pairings, so the mRNA would move relative to the ________.
Codon-anticodon; ribosome
During prokaryotic termination, what binds to stop codons?
Release factors (RF1 and RF2)
During termination, what is RF-3-GTP and what does it do?
It is a small GTP-binding protein, and it facilitates the binding of RF-1 or RF-2 to the ribosome.
What are the steps in prokaryotic translation termination?
1. RF-1 or RF-2 recognize and bind to the stop codon, with RF-3-GTP facilitating the binding.
2. When the release factors occupy the A-site, the ribosomal peptidyl transferase catalyzes the transfer of the peptidyl group to water (hydrolysis).
3. Hydrolysis of GTP on RF-3 (to GDP + Pi) causing a conformational change that results in dissociation of the release factors.
4. RRF (ribosomal recycling factor), along with EF-G-GTP and IF-3, facilitate the release of the uncharged tRNA from the P site and the dissociation of the ribosome from the mRNA (with the separation of the two ribosomal subunits).
When the last tRNA is released in translation termination, what happens to the peptide bond?
It is hydrolyzed.
What are the two major differences between eukaryotic and prokaryotic translation?
1. There are three initiating factors in prokaryotic translation; there are at least 11 in eukaryotic translation.
2. Finding the start codon
Prokaryotes: The Shine-Dalgarno sequence on the message base pairs with a sequence on the rRNA of the small subunit. This base pairing orients the start codon in the P site of the ribosome. After the message is bound, initiator tRNA binds.
Eukaryotes: The initiator tRNA binds to the ribosome first (the small subunit has no affinity for the message). Initiation factors bind to the ends of the mRNA and deliver it to the ribosome. These initiation factors use the bound initiator tRNA to find the start codon on the mRNA and set the reading frame.
How many elongation factors are involved in eukaryotic translation?
Two, eEF1 and eEF2
True or False: Both eukaryotic and prokaryotic ribosomes have A,P, and E sites.
False; eukaryotic ribosomes lack an E site.