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Related Concept Videos

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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The Nucleosome02:33

The Nucleosome

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DNA in a human cell is almost 2m long and it is packed inside a tiny nucleus that is only a few microns in diameter. The level of compaction of DNA inside the nucleus is astonishing. It is organized into several sequentially higher levels of compaction to 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.
DNA is wound twice around a protein complex called histone core, that consist of 8 histone proteins. This complex...
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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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Chromatin Packaging02:21

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, which means that each diploid cell contains a staggering 2 meters of DNA. How is such a long DNA strand packed inside a nucleus measuring only 10 - 20 microns in diameter? 
The chromatin
In combination with specialized DNA binding protein called Histones, the DNA double helix forms a compact DNA: protein complex called chromatin. The chromatin itself is further compacted into higher-order...
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DNA Packaging00:58

DNA Packaging

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Overview
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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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Related Experiment Video

Updated: Feb 26, 2026

Mapping Absolute DNA Density in Cell Nuclei using Single-molecule Localization Microscopy
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Mapping Absolute DNA Density in Cell Nuclei using Single-molecule Localization Microscopy

Published on: November 11, 2025

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An Extraordinarily Stable DNA Minidumbbell.

Pei Guo1, Sik Lok Lam1

  • 1Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong.

The Journal of Physical Chemistry Letters
|July 12, 2017
PubMed
Summary

Minidumbbells (MDBs) are novel DNA structures. Researchers found that CCTG repeats form a highly stable MDB at pH 5.0, enabling pH-controlled DNA structural switching.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • Minidumbbells (MDBs) are native DNA structures formed by repeat sequences.
  • MDBs are implicated as intermediates in DNA repair and repeat expansion diseases.
  • Previous studies showed MDBs formed by TTTA or CCTG repeats have low melting temperatures (~22 °C) at neutral pH.

Purpose of the Study:

  • To investigate the structural stability of CCTG repeat-containing MDBs at acidic pH.
  • To explore the potential of CCTG MDBs as pH-responsive molecular switches.

Main Methods:

  • DNA structure analysis
  • Melting temperature measurements
  • pH-dependent structural conversion assays

Main Results:

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  • Two CCTG repeats formed an exceptionally stable MDB at pH 5.0 with a melting temperature of ~46 °C.
  • This stability is attributed to a three-hydrogen bond C+·C mispair in the minor groove.
  • The CCTG MDB system exhibited rapid and complete structural conversions between pH 5.0 and 7.0.

Conclusions:

  • CCTG repeat MDBs display significantly enhanced thermodynamic stability at acidic pH.
  • The pH-dependent stability of CCTG MDBs allows for efficient, reversible molecular switching.
  • This finding opens avenues for developing novel pH-controlled DNA-based nanodevices.