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Cell structure - Nucleus - DNA Condensation
DNA Condensation
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| Description |
The total length of the DNA in a human cell is approximately 2 meters. The DNA double strand that is wound into an alpha helix only fits into the cellular nucleus, because it is folded in a complex manner. Structural proteins are required for this folding; together with the DNA they are termed chromatin.
Octamers comprised of histones bind to DNA, which wraps itself around this protein core in the process: thus forming a nucleosome. Between adjacent nucleosomes a piece of DNA, the linker DNA, remains free. Consequently, a characteristic "string of pearls structure" is formed.
The nucleosome chain is folded to form a 30-nanometer fibre. An additional structural protein, histone 1, stabilises this fibre. Certain regions of the 30-nanometer fibre, the "scaffold associated regions" couple to structural proteins, among them the topoisomerase. In this process the 30-nanometer fibre forms loops.
The filamentous DNA-Protein complex forms the so-called supertwist, which is further twisted in an additional coiling step. With this final step the complete condensation of chromatin has been achieved. This is the organisational state of the chromosome during nuclear division, mitosis.
Outside of the phases of division the chromosomes are partially decondensed. In this manner the DNA strands are accessible for reading their genetic information and for replication.
Duration: 02:21 min
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Sources
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BEREITER-HAHN, JÜRGEN; PETERS, WINFRIED S.: Nucleus of Life - From Gene to Protein. CD-ROM C 7103. MMcD, Düsseldorf; interActive Systems iAS, Marburg, Berlin; IWF, Göttingen, 2003.
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Abbreviations
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Order |
This film is part of the CD-ROM Nucleus of Life - From Genes to Proteins. You can order it at the IWF Knowledge and Media gGmbH.
Also available as clip.
Order no.:
C 13105
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