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Related Concept Videos

Ribosomal RNA Synthesis02:53

Ribosomal RNA Synthesis

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Ribosome synthesis is a highly complex and coordinated process involving more than 200 assembly factors. The synthesis and processing of ribosomal components occurs not only in the nucleolus but also in the nucleoplasm and the cytoplasm of eukaryotic cells.
Ribosome biogenesis begins with the synthesis of 5S and 45S pre-rRNAs by distinct RNA polymerases. The primary transcripts are extensively processed and modified before they are bound and folded by ribosomal proteins and assembly factors,...
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Ribosomes01:27

Ribosomes

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Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.
Ribosome Structure and Assembly
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Initiation of Translation02:33

Initiation of Translation

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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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Microtubule Formation01:23

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Microtubules are dynamic structures that undergo continuous assembly and disassembly. They originate from specialized multi-protein complexes known as microtubule organizing centers or MTOCs. Within the MTOC, the point of origin of the microtubule is known as the minus end, while the end radiating outward is the plus end. Microtubules serve two primary functions — the organization of spindle complexes to separate sister chromatids during mitotic or meiotic cell division and the formation...
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Bacterial Protein Maturation01:26

Bacterial Protein Maturation

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Bacterial protein maturation is a tightly regulated process that ensures newly synthesized polypeptides achieve correct functional conformations. This maturation involves a series of modifications, folding events, and quality control steps, often assisted by specialized chaperone proteins.N-Terminal ModificationsThe maturation of bacterial polypeptides begins cotranslationally as the polypeptide exits the ribosome. The first amino acid, N-formylmethionine (fMet), is typically modified at the...
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Termination of Translation01:44

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The large ribosomal subunit has several important structures essential to translation. These include the peptidyl transferase center (PTC) - which is the site where the peptide bond is formed - and a large, internal, water-filled tube through which the nascent polypeptide moves. This latter structure is called the Peptide Exit Tunnel, and it begins at the PTC and spans the body of the large ribosomal subunit. During translation, as the nascent polypeptide chain is synthesized, it passes through...
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Related Experiment Video

Updated: Oct 6, 2025

Rapid Isolation of the Mitoribosome from HEK Cells
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Mitoribosomal small subunit maturation involves formation of initiation-like complexes.

Tea Lenarčič1, Moritz Niemann2, David J F Ramrath1

  • 1Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, CH-8093 Zurich, Switzerland.

Proceedings of the National Academy of Sciences of the United States of America
|January 19, 2022
PubMed
Summary

Mitochondrial ribosome assembly in Trypanosoma brucei reveals conserved steps and factors. New structures show how assembly factors and mitochondrial initiation factor 2 (mt-IF-2) guide small subunit maturation.

Keywords:
mitochondriaribosome assemblystructural biologytranslation

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Area of Science:

  • Cell Biology
  • Structural Biology
  • Biochemistry

Background:

  • Mitochondrial ribosomes (mitoribosomes) synthesize essential inner membrane proteins for oxidative phosphorylation.
  • Mitoribosome structure varies across organisms, but assembly principles appear conserved.
  • Understanding mitoribosome assembly is key to deciphering mitochondrial function.

Purpose of the Study:

  • To investigate the assembly pathway of the mitochondrial small subunit (mt-SSU) in Trypanosoma brucei.
  • To elucidate the roles of assembly factors and initiation factors in mt-SSU maturation.

Main Methods:

  • Cryoelectron microscopy (cryo-EM) to determine structures of assembly intermediates.
  • RNA interference (RNAi) experiments to validate factor functions.

Main Results:

  • Determined cryo-EM structures of mt-SSU assembly intermediates at 3.6- and 3.7-Å resolution.
  • Identified five novel assembly factors interacting with key rRNA regions.
  • Showed that mitochondrial initiation factor 2 (mt-IF-2) has a noncanonical role in preventing premature subunit association.

Conclusions:

  • Mitoribosome small subunit assembly proceeds through distinct intermediate stages.
  • Conserved assembly factors and mt-IF-2 are crucial for proper rRNA folding and protein maturation.
  • The findings provide insights into the stepwise and modular nature of mitoribosome biogenesis.