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Related Concept Videos

The Mitotic Spindle02:27

The Mitotic Spindle

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The mitotic spindle—or spindle apparatus—is a eukaryotic, cytoskeletal structure made up of long protein fibers called microtubules. Formed during cell division, the spindle separates sister chromatids and moves them to opposite ends of a parental cell, where the now individual chromosomes are distributed to two daughter cell nuclei.
The bipolar configuration of the mitotic spindle facilitates chromosomal segregation, preparing the cell for division. One mechanism that ensures...
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Chromosome Structure02:40

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A functional eukaryotic chromosome must contain three elements: a centromere, telomeres, and numerous origins of replication.
The centromere is a DNA sequence that links sister chromatids. This is also where kinetochores, protein complexes to which spindle microtubules attach, are constructed after the chromosome is replicated. The kinetochores allow the spindle microtubules to move the chromosomes within the cell during cell division.
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In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome duplication, chromosome distribution to daughter cells, and finally, cell division. The cell cycle is tightly regulated by its regulatory systems as well as extracellular signals that affect cell proliferation.
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Forces Acting on Chromosomes02:11

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During mitosis, chromosome movements occur through the interplay of multiple piconewton level forces. In prometaphase, these forces help in chromosome assembly or congression at the equatorial plane, eventually leading to their alignment at the metaphase plate. The forces acting on the chromosomes are space and time-dependent; therefore, they vary with the position of the chromosomes as the cell progresses through mitosis. 
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Attachment of Sister Chromatids02:57

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As cells progress into mitosis, the nuclear envelope breaks down, and the condensed chromosomes are exposed to the array of bipolar microtubules of the mitotic spindle. The kinetochore, a large, disc-shaped protein complex, is present at the centromere region of the sister chromatids and acts as a binding site for the microtubules.  Usually, the plus-end of a single microtubule is embedded within the kinetochore. However, some kinetochores first establish lateral contact with the side-wall...
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Meiosis vs. Mitosis02:57

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Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
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Related Experiment Video

Updated: Oct 20, 2025

Examination of Mitotic and Meiotic Fission Yeast Nuclear Dynamics by Fluorescence Live-cell Microscopy
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Structure of mitotic chromosomes.

Andrew J Beel1, Maia Azubel1, Pierre-Jean Matteï1

  • 1Department of Structural Biology, Stanford University, Stanford, CA 94305, USA.

Molecular Cell
|September 14, 2021
PubMed
Summary

Chromatin fibers in condensed chromosomes show irregular trajectories, not the expected coiling. This study visualizes the internal structure of mitotic chromosomes at high resolution, revealing nucleosome details and DNA fiber paths.

Keywords:
chromatin fiberschromosome condensationcryo-electron tomographymitotic chromosomes

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Examination of Mitotic and Meiotic Fission Yeast Nuclear Dynamics by Fluorescence Live-cell Microscopy
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Live Cell Imaging to Assess the Dynamics of Metaphase Timing and Cell Fate Following Mitotic Spindle Perturbations
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Live Cell Imaging to Assess the Dynamics of Metaphase Timing and Cell Fate Following Mitotic Spindle Perturbations

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Genetics

Background:

  • Chromosome condensation involves chromatin fiber folding or coiling.
  • Previous studies visualized coiling patterns in reconstituted chromatin.
  • High material density in condensed chromosomes limited visualization of internal fiber trajectories.

Purpose of the Study:

  • To visualize the internal structure of condensed mitotic chromosomes at sub-nucleosomal resolution.
  • To determine the actual trajectories of chromatin fibers within chromosomes.
  • To identify the native state of nucleosomes and their arrangement.

Main Methods:

  • Utilized partial decondensation of mitotic chromosomes.
  • Employed cryo-electron tomography for high-resolution imaging.
  • Avoided stains, fixatives, milling, or sectioning to preserve native structure.

Main Results:

  • Visualized DNA gyres around nucleosomes, enabling identification and orientation determination.
  • Traced linker DNA regions, revealing irregular chromatin fiber trajectories.
  • Observed no significant coiling or short/long-range order in chromosomal material.
  • Identified the 146-bp core particle as the native nucleosome state without regular spacing.

Conclusions:

  • Chromatin fibers in condensed chromosomes exhibit irregular, non-coiled trajectories.
  • The native nucleosome is the 146-bp core particle, lacking regular spacing along fibers.
  • Cryo-electron tomography provides unprecedented insight into chromosome internal organization.