12 Translation

1. Which eukaryotic initiation factor is responsible for directly recognizing and binding the m7G cap of the mRNA?

eIF4E
eIF4A
eIF4G
eIF2

2. In the presence of high iron concentrations, what structural change occurs in the Iron Regulatory Protein (IRP)?

It becomes phosphorylated by PERK to increase its affinity for mRNA
It adopts a [4Fe−4S] cluster conformation unsuitable for IRE binding
It triggers the cleavage of the poly-A tail to destabilize the mRNA
It binds to the 60S subunit to block the exit tunnel

3. In prokaryotic ribosome recycling, what is the role of the Ribosome Recycling Factor (RRF)?

It recruits EF-G-GTP to stimulate the release of tRNAs from the P and E sites.
It phosphorylates IF3 to signal the end of the recycling process.
It acts as a chaperone to refold the newly synthesized protein.
It binds to the E site to eject the uncharged tRNA.

4. In the diagram of mRNA-specific control, what is ‘uORF’?

A universal Organelle Reading Frame.
A unit of Ribosomal Function.
An unfolded RNA fragment that inhibits the ribosome.
An upstream Open Reading Frame that can regulate translation of the main downstream coding sequence.

5. During translation elongation, what is the role of Elongation Factor Tu (EF−Tu)?

To deliver aminoacyl-tRNAs to the A site and prevent premature peptide bond formation
To facilitate the translocation of the peptidyl-tRNA from the A site to the P site
To catalyze the formation of the peptide bond between the A and P sites
To recycle the ribosome by dissociating the subunits after termination

6. What is the role of RNA helicases in eukaryotic translation initiation?

To remove the 5′ cap once the ribosome has successfully loaded
To catalyze the translocation of the ribosome during elongation
To resolve secondary structures in the mRNA during the scanning process
To proofread the codon-anticodon pairing in the P site

7. Which of the following is an example of transcript-specific (cis-acting) translational control?

The binding of a regulatory protein to a specific stem-loop structure in the 5′ UTR of a single mRNA type.
The depletion of the total cellular pool of GTP.
The activation of mTORC1 to phosphorylate 4E-BPs.
Global phosphorylation of eIF2α by PKR during viral infection.

8. How do Class I Release Factors (e.g., RF1) trigger the release of the completed polypeptide chain?

By phosphorylating the large ribosomal subunit to induce a conformational change
By binding to the E site and blocking further tRNA entry
By utilizing GTPase activity to physically pull the polypeptide through the exit tunnel
By mimicking the structure of a tRNA and activating hydrolysis of the peptidyl-tRNA bond

9. Which initiation factor in prokaryotes blocks the A site during the assembly of the 30S complex?

IF1
IF2
IF3
EF−Tu

10. What is the specific function of eIF4E in the eukaryotic initiation complex?

It delivers the initiator tRNA to the P site of the 40S subunit.
It directly binds to the 7-methylguanylate cap at the 5′ end of the mRNA.
It recognizes the Kozak sequence to stop the scanning process.
It hydrolyzes ATP to unwind RNA secondary structures.

11. What is the consequence of eIF2α phosphorylation at Serine 51?

It increases the affinity of eIF2 for the initiator tRNA, accelerating translation
It sequesteres eIF2B, preventing the exchange of GDP for GTP on eIF2
It causes eIF2 to bind the 3′ UTR instead of the 5′ cap
It triggers the rapid degradation of all cellular mRNAs by activating RNases

12. What is the function of the Kozak sequence in eukaryotic translation?

To bind EF−Tu and facilitate the first peptide bond
To act as a binding site for the N-formyl-methionine tRNA
To signal the termination of translation and recruitment of RF1
To help the scanning ribosome identify the correct start codon

13. During elongation, why does EF-Tu mask the amino acid coupled to the tRNA?

To prevent peptide bond formation before the tRNA is properly positioned and EF-Tu is released.
To signal to the P site that the A site is now occupied.
To allow the tRNA to fit through the narrow entry channel of the ribosome.
To prevent the amino acid from being degraded by cytoplasmic proteases.

14. In the regulation of ferritin translation, how does the Iron Regulatory Protein (IRP) respond to low cellular iron levels?

It undergoes degradation, allowing for the constitutive translation of ferritin mRNA
It binds to the Iron Response Element (IRE) in the 5′ UTR, blocking 43S complex recruitment
It recruits mTORC1 to phosphorylate 4E−BP, stimulating translation
It acts as a helicase to assist the ribosome in scanning through the IRE hairpin

15. During the recycling of prokaryotic ribosomes, what does RRF recruit to help release uncharged tRNAs?

eIF4E
RF1
EF-G-GTP
IF2-GTP

16. What is the role of Class II release factors, such as RF3?

They catalyze the hydrolysis of the peptide from the tRNA.
They promote the dissociation of Class I release factors from the ribosome.
They recognize the UAG stop codon and bind to it directly.
They help the small subunit find the start codon in prokaryotes.

17. Which kinase is specifically activated by viral infection to phosphorylate eIF2α and inhibit global translation?

GCN2
PERK
PKR
mTORC1

18. Which molecule is released from the complex immediately after the large ribosomal subunit binds during prokaryotic initiation?

IF2-GTP
16S rRNA
The initiator tRNA
IF3

19. If a mutation occurred in the factor-binding center of the ribosome such that it could no longer activate GTPase activity, which step of elongation would be most directly stalled?

The formation of the peptide bond by the 23S rRNA.
The release of EF-Tu from the aminoacyl-tRNA in the A site.
The binding of the mRNA to the small subunit.
The exit of uncharged tRNA from the E site.

20. How does the hypophosphorylated state of 4E−BP affect eukaryotic translation?

It catalyzes the scanning of the mRNA to find the start codon
It serves as a scaffold to bring the 60S and 40S subunits together
It enhances the recruitment of the poly-A binding protein to the 3′ end
It binds to eIF4E, preventing its interaction with eIF4G and blocking initiation

21. True or False: EF−Tu prevents peptide bond formation until it is released from the tRNA.

False
True

22. Which kinase is specifically activated by endoplasmic reticulum (ER) stress to inhibit global translation?

PKR
GCN2
PERK
mTORC1

23. What happens to the prokaryotic initiator tRNA (fMet-tRNA) during the very first step of translation elongation?

It moves from the A site to the P site via EF−G mediation
It is immediately ejected from the E site before the second tRNA arrives
It is modified by IF1 to ensure it cannot participate in further elongation cycles
The peptide bond forms, leaving the deacylated fMet-tRNA in the P site

24. In prokaryotic translation initiation, what is the specific role of the 16S rRNA within the small ribosomal subunit?

It catalyzes the formation of the first peptide bond between fMet and the second amino acid.
It base pairs with a specific sequence on the mRNA to recruit and position the ribosome.
It acts as a GTPase-activating protein for the initiation factor IF2.
It masks the start codon to prevent premature binding of the initiator tRNA.

25. In the context of the Ferritin IRE/IRP system, what type of sequence/structure is the ‘IRE’?

A cis-regulatory RNA element.
A trans-acting protein factor.
A specialized ribosomal protein.
A modified form of the 5′ cap.

26. According to the study by Schwanhäusser et al., which process is the single best predictor of absolute protein levels in mammalian cells?

mRNA half-life
Nuclear export speed
Transcription rate
Translation efficiency

27. During the assembly of the prokaryotic 30S initiation complex, what prevents the 50S subunit from binding prematurely?

The masking of the 16S rRNA by IF1.
The presence of IF3 bound to the small subunit.
The hydrolysis of GTP by IF2.
The binding of the initiator tRNA to the A site.

28. What is the eukaryotic equivalent of the prokaryotic IF2-GTP function regarding tRNA placement?

eIF4A unwinding the mRNA.
eIF2-GTP binding to Met-tRNA and the small subunit.
eIF5B stimulating large subunit joining.
eIF4E binding to the cap.

29. Which set of factors is required for ribosome recycling in prokaryotes after the polypeptide has been released?

RRF, EF−G, and IF3
EF−Tu and aminoacyl-tRNA synthetase
RF1, RF2, and RF3
eIF4E, eIF4G, and eIF4A

30. How does the recruitment of the small ribosomal subunit differ between prokaryotes and eukaryotes?

In eukaryotes, the small subunit is already associated with the initiator tRNA when it binds the 5′ cap.
In eukaryotes, the small subunit is recruited to the 3′ poly-A tail first.
In prokaryotes, a helicase must clear the 5′ UTR before the 30S subunit can bind.
In prokaryotes, the initiator tRNA is already bound to the small subunit before mRNA recruitment.

31. Why is the scanning process necessary in eukaryotic translation initiation but not in prokaryotic initiation?

Eukaryotic mRNAs lack a 5′ UTR.
Prokaryotes do not use methionine as their first amino acid.
Prokaryotic mRNAs use 16S rRNA base pairing to 'anchor' the ribosome directly at the start site.
Eukaryotic ribosomes are too large to bind directly to the start codon.

32. In the context of mRNA-specific control, what is an IRES?

Initiator RNA Enhancement Segment
Internal Ribosome Entry Site
Iron-Regulated Elongation Sequence
Inhibitory Ribosomal Exit Structure

33. What is the biochemical consequence of eIF2α phosphorylation at Ser 51?

It stabilizes the interaction between eIF2 and its exchange factor eIF2B, sequestering both.
It increases the affinity of eIF2 for GTP, leading to over-active initiation.
It prevents eIF4E from binding to the 5′ cap of the mRNA.
It triggers the immediate degradation of the initiator Met-tRNA.

34. In the Schwanhäusser model of gene expression, which factor showed the least correlation with protein half-lives?

Translation rates
Transcription rates
mRNA half-lives
mRNA levels

35. What is the structural modification found on the initiator tRNA in prokaryotes?

3′ poly-adenylation
Acetylated Lysine
7-methylguanosine
N-formyl-methionine

36. How do 4E-binding proteins (4E-BPs) inhibit translation initiation when they are hypophosphorylated?

They act as RNAses that specifically degrade the 5′ cap.
They phosphorylate eIF4A to inhibit its helicase activity.
They bind to the 40S subunit and block the exit site.
They compete with eIF4G for binding to eIF4E.

37. What role does the ‘Kozak sequence’ play in eukaryotic translation?

It acts as a binding site for the poly-A binding protein.
It is the sequence surrounding the AUG that determines the efficiency of start codon recognition.
It provides the energy required for the helicase to unwind the RNA.
It is the site where the large subunit first contacts the mRNA.

38. True or False: During translation elongation, tRNAs enter the ribosome at the P site.

False
True

39. In the regulation of ferritin mRNA, what occurs when cellular iron levels are high?

An iron-sulfur cluster [4Fe−4S] forms in the IRP, preventing it from binding the IRE.
The IRE sequence is spliced out of the mRNA, allowing constitutive translation.
The Iron Regulatory Protein (IRP) binds to the Iron Response Element (IRE), blocking translation.
IRP targets the ferritin mRNA for immediate degradation in the P-body.

40. During translocation, EF-G-GTP hydrolysis provides the energy to:

Form the peptide bond between the A and P site amino acids.
Recruit IF3 to the small subunit.
Bind the next aminoacyl-tRNA to the A site.
Move the peptidyl-tRNA from the A site to the P site.

41. In prokaryotic translation initiation, which component of the small ribosomal subunit is responsible for recruiting mRNA through base pairing?

Initiation Factor 2 (IF2)
16S rRNA
5S rRNA
23S rRNA

42. Which factor binding center interaction triggers the GTPase activity of EF−Tu?

The mRNA's 3′ UTR sequence
The ribosome's factor binding center
The eIF4G scaffold protein
The Class II Release Factor RF3

43. Which elongation factor is responsible for delivering aminoacyl-tRNA to the A site and ensuring its correct pairing?

IF2
EF-Tu
EF-G
RF3

44. Which initiation factor is released immediately before or upon the binding of the large ribosomal subunit in prokaryotes?

EF-Tu
IF3
RRF
IF1

45. What is the primary function of Initiation Factor 3 (IF3) during the assembly of the prokaryotic translation complex?

To deliver the N-formyl-methionine tRNA to the A site
To catalyze the hydrolysis of GTP to provide energy for mRNA scanning
To prevent the large subunit from prematurely associating with the small subunit
To recognize and bind the 5′ cap structure of the mRNA

46. What defines a ‘Class II’ Release Factor such as RF3?

It binds to the 16S rRNA to stabilize the mRNA during release
It catalyzes the formation of the last peptide bond in the chain
It stimulates the dissociation of Class I factors from the ribosome using GTP
It recognizes the stop codon sequence UAA directly

47. What structural feature allows Class I release factors (like RF1) to trigger the release of the polypeptide chain?

They mimic the structure of a tRNA molecule to enter the A site.
They are GTPases that provide the energy for ribosomal dissociation.
They possess intrinsic protease activity that cleaves the peptide bonds.
They contain a specific RNA sequence that base pairs with the stop codon.

48. Which molecule is responsible for bringing the modified methionine (fMet) to the P site in prokaryotes?

An elongation factor complexed with GTP.
The 16S rRNA molecule itself.
A standard methionyl-tRNA that enters through the A site.
Initiator tRNA (fMet-tRNA) delivered by IF2.

49. In eukaryotes, how does the recruitment of the small ribosomal subunit to mRNA differ significantly from the prokaryotic process?

The large subunit binds the mRNA first to create a scaffold for the small subunit
The small subunit is already associated with the initiator tRNA before reaching the mRNA
Initiator tRNA enters the A site instead of the P site during eukaryotic initiation
The small subunit recognizes a specific internal ribosome-binding site via 18S rRNA

50. Which of the following is a ‘cis-acting’ element in translational control?

A ribosome-binding protein complex
The Iron Regulatory Protein (IRP)
The mTORC1 kinase complex
An Iron Response Element (IRE) hairpin loop

51. According to the Schwanhäusser et al. study, which process is the best predictor of absolute protein levels in mammalian cells?

Translation efficiency
mRNA half-life
Nuclear export speed
Transcription rate

52. What is the primary difference between global and transcript-specific translational control?

Global control involves mRNA degradation, while specific control involves protein folding.
Transcript-specific control only occurs in prokaryotes.
Global control acts on general initiation factors, while specific control involves regulatory proteins binding unique mRNA elements.
Global control is only used during cell death (apoptosis).