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Related Concept Videos

Improving Translational Accuracy02:07

Improving Translational Accuracy

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Base complementarity between the three base pairs of mRNA codon and the tRNA anticodon is not a failsafe mechanism. Inaccuracies can range from a single mismatch to no correct base pairing at all. The free energy difference between the correct and nearly correct base pairs can be as small as 3 kcal/ mol. With complementarity being the only proofreading step, the estimated error frequency would be one wrong amino acid in every 100 amino acids incorporated. However, error frequencies observed in...
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Proofreading01:31

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Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template DNA strand. DNA polymerase has a higher affinity to add the correct base and ensures fidelity during DNA replication. Furthermore,  it exhibits proofreading activity during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.
Errors During Replication are Corrected by the DNA Polymerase...
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tRNA Activation02:26

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Aminoacyl-tRNA synthetases are present in both eukaryotes and bacteria. Though eukaryotes have 20 different aminoacyl-tRNA synthetases to couple to 20 amino acids, many bacteria do not have genes for all of these aminoacyl-tRNA synthetases. Despite this, they still use all 20 amino acids to synthesize their proteins. For instance, some bacteria do not have the gene encoding the enzyme that couples glutamine with its partner tRNA. In these organisms, one enzyme adds glutamic acid to all of the...
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During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA.  Marilyn Kozak discovered that the sequence RCCAUGG (where R...
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Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
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Transfer RNA Synthesis02:36

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One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the molecule. Altogether, these unusual bases protect the tRNA from enzymatic degradation by RNases.
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Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses
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Human Protein Synthesis Requires aminoacyl-tRNA Pivoting During Proofreading.

Divya Sapkota1,2, Karissa Sanbonmatsu3,4, Dylan Girodat1,5

  • 1Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas, 72701, USA.

Biorxiv : the Preprint Server for Biology
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Summary

Human translation involves a unique ~30° pivot of aminoacyl-tRNA (aa-tRNA) during accommodation, crucial for ribosomal accuracy. This movement, alongside eEF1A interactions, ensures precise alignment and enhances translational fidelity.

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Biochemistry

Background:

  • Bacterial tRNA selection is well-characterized, but human mechanisms differ, featuring subunit rolling and slower proofreading.
  • Previous studies identified key intermediates but lacked insight into tRNA transitions during selection.

Purpose of the Study:

  • To elucidate the dynamic transitions of aminoacyl-tRNA (aa-tRNA) during accommodation into the human ribosomal A site.
  • To understand the structural basis for distinct human aa-tRNA selection mechanisms compared to bacteria.

Main Methods:

  • Simulated 1,856 aa-tRNA accommodation events into the human ribosomal A site.
  • Analyzed the structural dynamics and interactions during aa-tRNA entry.

Main Results:

  • Identified a critical ~30° pivot of aa-tRNA about its anticodon stem within the accommodation corridor.
  • Demonstrated that subunit rolling-dependent crowding necessitates this pivoting for aa-tRNA navigation.
  • Revealed that domain III of eEF1A interacts with aa-tRNA, preventing premature dissociation.

Conclusions:

  • The aa-tRNA pivot is essential for navigating the constrained human ribosomal A site, contributing to translational fidelity.
  • Human aa-tRNA selection involves distinct structural dynamics, including pivoting and eEF1A interactions, differing from bacterial mechanisms.