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Related Concept Videos

Ribosomes01:27

Ribosomes

77.7K
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
Ribosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome...
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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
Ribosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome...
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Translation01:31

Translation

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Lesson: Translation
Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes the final step in the expression of genes. This process is carried out by ribosomes, complexes of protein and specialized RNA molecules. Ribosomes, transfer RNA (tRNA), and other proteins produce a chain of amino acids—the polypeptide—as the end product of translation.
Translation Produces the Building Blocks of...
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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.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
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Termination of Translation01:44

Termination of Translation

27.9K
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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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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Polyribosomes of circular topology are prevalent in mammalian cells.

Nucleic acids research·2022
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Updated: Feb 14, 2026

Analysis of Translation Initiation During Stress Conditions by Polysome Profiling
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Analysis of Translation Initiation During Stress Conditions by Polysome Profiling

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Circularization and Ribosome Recycling: From Polysome Topology to Translational Control.

Zhanna A Afonina1, Konstantin S Vassilenko1

  • 1Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Russia.

International Journal of Molecular Sciences
|February 13, 2026
PubMed
Summary

Eukaryotic messenger RNAs form circular polysomes, enhancing protein synthesis through closed-loop-assisted reinitiation (CLAR). This dynamic structure balances translation efficiency with linear arrangements depending on cellular conditions.

Keywords:
eukaryotic translationmRNA cyclizationpolysomeribosome recyclingtranslation reinitiation

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Eukaryotic messenger RNAs (mRNAs) are translated by multiple ribosomes forming polysomes.
  • Polysomes exhibit diverse topologies, including circular arrangements, as proposed by the closed-loop model.
  • The closed-loop model suggests spatial proximity of mRNA termini facilitates ribosome recycling.

Purpose of the Study:

  • To investigate the structural conformations of polysomes.
  • To provide mechanistic insights into mRNA circularization and ribosome recycling.
  • To understand the role of mRNA topology in translational control.

Main Methods:

  • Biochemical assays
  • Structural biology techniques (electron microscopy, atomic force microscopy, cryo-electron tomography)
  • Single-molecule fluorescence imaging
  • Ribosome turnover experiments
  • Kinetic analyses and computational modeling

Main Results:

  • Polysomes adopt compact and heterogeneous conformations.
  • Circular polysome assemblies constitute a significant fraction of observed structures.
  • Evidence supports closed-loop-assisted reinitiation (CLAR) for efficient ribosome recycling.
  • mRNA circularization is a dynamic, regulated state enhancing protein synthesis under specific conditions.

Conclusions:

  • mRNA circularization is a key regulatory mechanism influencing protein synthesis efficiency.
  • Polysome architecture, including circular and linear forms, dynamically balances translational control.
  • Further research is needed to understand the interplay between mRNA topology, ribosome dynamics, and translation.