Translation Processes in Molecular Biology

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Questions and Answers

What is the role of eIF2 in the initiation of translation in eukaryotes?

It forms a closed loop with the cap and polyA tail.

It blocks the P site for incoming tRNA.

It recruits aminoacyl-tRNA to the ribosome.

It hydrolyzes GTP when the start site is recognized. (correct)

Which factor is primarily responsible for blocking the A site during the initiation process in eukaryotes?

eIF1 (correct)

eIF3

eIF2

eIF5b

What initiates the peptide bond formation during elongation in the ribosome?

A dependent transfer from the P-site tRNA

Interaction of rRNA with the tRNA

GTP hydrolysis by eEF-Tu

A 2'OH nucleophile attack on the aminoacyl ester bond (correct)

What triggers the termination of translation?

Recognition of a stop codon by release factors Signup and view all the answers

Which process involves the degradation of mRNA containing premature stop codons?

Nonsense mediated decay Signup and view all the answers

How does antibiotic resistance arise during elongation?

Mutations in the rRNA gene and r-proteins Signup and view all the answers

What is the primary role of polypurine tracts in prokaryotic translation initiation?

They enhance binding of the small ribosomal subunit. Signup and view all the answers

Which factor is equivalent to IF2 in prokaryotes during large subunit joining in eukaryotes?

eIF5b Signup and view all the answers

What is the role of elongation factors (EFs) during protein synthesis?

They facilitate the formation of peptide bonds between amino acids. Signup and view all the answers

Which statement accurately describes termination in protein synthesis?

The process of termination correctly identifies a stop codon and releases the polypeptide chain. Signup and view all the answers

What is the main function of polysome profiling in the study of translation?

To analyze the distribution of ribosomes on mRNA molecules. Signup and view all the answers

What is nonsense-mediated decay (NMD)?

A cellular mechanism that degrades mRNA containing premature stop codons. Signup and view all the answers

Which component is responsible for charging tRNA with its respective amino acid?

Aminoacyl-tRNA synthetase Signup and view all the answers

During ribosome recycling, what happens after the polypeptide chain is released?

The ribosome disassembles into its large and small subunits. Signup and view all the answers

What occurs at the A site of the ribosome during translation elongation?

Incoming tRNA carries the next amino acid to be added to the polypeptide. Signup and view all the answers

Which of the following statements regarding the fidelity of protein synthesis is true?

Fidelity ranges from $10^{-2}$ to $10^{-5}$ based on various factors. Signup and view all the answers

What is the primary function of EF-G during translation?

To facilitate the movement of the mRNA:tRNA complex Signup and view all the answers

Which release factor in prokaryotes is responsible for recognizing the UAG and UAA stop codons?

RF1 Signup and view all the answers

What defines the main distinction between polysome profiling and ribosome profiling?

Ribosome profiling focuses on mRNA protected by ribosomes Signup and view all the answers

What happens during nonsense-mediated decay (NMD)?

NMD eliminates mRNAs that incorrectly terminate translation Signup and view all the answers

Which molecule hydrolyzes GTP to release the polypeptide chain during termination in eukaryotes?

eRF3 Signup and view all the answers

What is the role of RRF in prokaryotic ribosome recycling?

To facilitate the separation of ribosomal subunits Signup and view all the answers

What represents a significant feature of polysome profiling?

It measures RNA absorbance at various fractions Signup and view all the answers

What is the significance of the pioneer round of translation in relation to NMD?

It identifies mRNAs with incorrect codons early Signup and view all the answers

Study Notes

Translation: Initiation, Elongation, and Termination

Translation speed varies, 20 amino acids per second in E. coli, 5-10 in S. cerevisiae.
Fidelity is between 10⁻² and 10⁻⁵.
Start codons include AUG.
Stop codons are UAG, UAA, and UGA.

tRNA Structure

Has a 3' CCA tail for amino acid attachment.
Contains a D-loop and T-loop, aiding 3D structure.
Has an anticodon loop, interacting with codons for specificity.
Anticodon doesn't recognize stop codons.
Acceptor end interacts with EF-Tu and ribosomal tRNA binding sites.

Aminoacyl-tRNA Synthetases

There's one synthetase for each amino acid.
Accuracy (adding correct amino acids to tRNA) is crucial.
Editing site removes incorrect amino acids.
Aminoacylation site adds amino acids to tRNA using ATP.
Two-step loading—activation and transfer.

Ribosomes

Bacterial ribosomes are 70S, composed of 50S and 30S subunits.
Eukaryotic ribosomes are 80S, composed of 60S and 40S subunits.
Ribosomes consist of RNA (majority) and proteins.
rRNA highly conserved across species, crucial for function.
rRNA sequences mediate interactions between large and small subunits.
Ribosome's active site is solely RNA (ribozyme), not protein, for catalysis
Important regions of rRNA include the large-small subunit interface and tRNA-binding sites. This provides the site for folding of the rRNA.

Translation Initiation

IFs (initiation factors) are critical.
IF1 blocks A site, IF3 blocks E site.
IF2 is involved in large subunit joining, GTP hydrolysis occurs upon the finding of AUG.
Bacteria use formyl-methionine (f-Met) as the initiator.
Eukaryotes use methionine (Met).
Initiation complex involves initiator tRNA, and initiation factors, then associates with the mRNA and small ribosomal subunit.

Translation Elongation

EF-Tu/eEF-1a (GTPases) load tRNAs.
Correct codon-anticodon matches are critical (faster GTP hydrolysis if correct).
Peptide bond formation is a ribozyme-catalyzed reaction.
Translocation moves the mRNA-tRNA complex.
EF-G/ eEF-2 (GTPases) is responsible for translocation.
GTP hydrolysis promotes translocation.

Translation Termination

Release factors (RFs) recognize stop codons.
RF1 recognizes UAG/UAA.
RF2 recognizes UGA/UAA.
RF3 stimulates RF1/RF2 activity.
GTP hydrolysis releases the polypeptide chain.
Requires recycling of ribosomes (separating small and large subunits).

Polysomes

Multiple ribosomes translate the same mRNA simultaneously.
Studying polysomes helps understand translation dynamics.

Nonsense-Mediated Decay (NMD)

NMD eliminates mRNAs with premature stop codons.
NMD occurs in the pioneer round of translation in mammalian cells.
Exon junctions in mRNA help identify premature stop codons.
NMD may use the EJC to identify premature termination codons (PTCs).
eRF1 and eRF3 identify the stop codon, and lead to the degradation of the mRNA.

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Description

This quiz covers key concepts in the translation process, including initiation, elongation, and termination of protein synthesis. It examines the structures of tRNA and the functions of aminoacyl-tRNA synthetases, as well as the differences between bacterial and eukaryotic ribosomes. Test your understanding of these fundamental processes in molecular biology.