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Related Concept Videos

DNA Packaging00:58

DNA Packaging

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Overview
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Chromatin Packaging01:32

Chromatin Packaging

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Each human somatic cell contains 6 billion base pairs of DNA. Each base pair is 0.34 nm long, meaning each diploid cell contains a staggering 2 meters of DNA. This long DNA strand is packed inside a nucleus measuring only 10-20 microns in diameter with the help of specialized DNA-binding proteins called histones. Together they form a compact DNA-protein complex called chromatin. The chromatin is further compacted into higher-order structures. The highest level of compaction is achieved during...
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The Nucleosome01:19

The Nucleosome

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Human DNA is almost two meters long. However, it is compressed inside a tiny nucleus measuring only a few microns in diameter. To make this degree of compaction possible, DNA is organized into several sequential levels so that it can fit into such a tiny space. The most compact form of DNA is a chromosome that can be seen under a microscope in a dividing cell.
In a chromosome, DNA is wound twice around a protein complex called a histone octamer core, which consists of 8 histone proteins. This...
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Genomic DNA in Eukaryotes00:58

Genomic DNA in Eukaryotes

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Eukaryotes have large genomes compared to prokaryotes. To fit their genomes into a cell, eukaryotic DNA is packaged extraordinarily tightly inside the nucleus. To achieve this, DNA is tightly wound around proteins called histones, which are packaged into nucleosomes that are joined by linker DNA and coil into chromatin fibers. Additional fibrous proteins further compact the chromatin, which is recognizable as chromosomes during certain phases of cell division.
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Euchromatin01:01

Euchromatin

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The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions take up more dye, appearing darker, while the less-compact areas take up less dye and appear lighter. Based on the compaction level, chromatins are classified into two primary forms – euchromatin and heterochromatin.
Euchromatin is the less dense region of the chromatin and stains lighter. Euchromatin contains histone H3 extensively...
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Nucleosome Remodeling02:54

Nucleosome Remodeling

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Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA inaccessible to DNA binding proteins such as DNA polymerase and RNA polymerase. Hence, the fundamental problem is to ensure access to DNA when appropriate, despite the compact and protective chromatin structure.
Nucleosome remodeling complex
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Related Experiment Video

Updated: Jul 8, 2025

Visualization of DNA Compaction in Cyanobacteria by High-voltage Cryo-electron Tomography
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Visualization of DNA Compaction in Cyanobacteria by High-voltage Cryo-electron Tomography

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Multiple modes of DNA compaction by protamine.

Vikhyaat Ahlawat1, Huan-Xiang Zhou1

  • 1Department of Chemistry and Department of Physics, University of Illinois Chicago, Chicago, United States.

Biorxiv : the Preprint Server for Biology
|December 18, 2023
PubMed
Summary

Protamine dramatically compacts sperm DNA, forming stable coils and loops. This extreme DNA compaction by protamine is crucial for gene silencing.

Area of Science:

  • Molecular Biology
  • Biophysics
  • Genetics

Background:

  • Sperm cells utilize protamine to achieve DNA compaction far exceeding somatic cells.
  • Understanding protamine's role is key to explaining extreme genome organization and transcriptional silencing in sperm.

Approach:

  • Confocal microscopy visualized DNA compaction at varying protamine concentrations.
  • Optical tweezers measured the mechanical stability and conformational changes of protamine-bound DNA.

Key Points:

  • Protamine binding induces DNA bending, looping, and coiling, shortening contour length by up to 40% and withstanding forces up to ~55 pN.
  • DNA strand separation initiates coiling, suggesting protamine inserts into DNA bases.
  • Protamine influences both local and higher-order chromatin structures.

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Tools to Study the Role of Architectural Protein HMGB1 in the Processing of Helix Distorting, Site-specific DNA Interstrand Crosslinks
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Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination
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Visualization of DNA Compaction in Cyanobacteria by High-voltage Cryo-electron Tomography
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Tools to Study the Role of Architectural Protein HMGB1 in the Processing of Helix Distorting, Site-specific DNA Interstrand Crosslinks
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Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination
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Conclusions:

  • Protamine mediates extreme DNA compaction in sperm through unique structural interactions.
  • This process is essential for achieving the high-density DNA packaging required for sperm function and global gene silencing.