DNA compaction
From ResearchID.org
The structure of the DNA within the cell, as explained by most textbooks, is a caricature of its actual compaction and structure. In a eukaryotic cell, the DNA undergoes many levels of twisting, folding, rolling, twirling, and coiling during replication, or meiosis. Most genetics textbooks present a summary, since many of these structural discoveries are on-going. Given the dense and complex compaction DNA undergoes, only providing a summary in a textbook is understandable, but does not due the process justice.
Here is a brief sketch:
- DNA is an encoded nucleotide sequence polymer with a
- double-helix structure that rests in the fibrous
- nuclear matrix where a
- histone is wrapped roundabout by DNA, wrapped histones are bundled by
- linker histones to form
- nucleosome which makes chains of a
- nucleosomal array which forms
- chromatin fibers and the
- chromatin scaffolding that takes its shape into
- chromatin scaffolding loops to become a
- chromosome which is the
- genetic material which is in the
- nucleolus which in turn is in the
- nucleus which is in a
- cell.
Video
- Other interesting DNA states
- The DNA supercoil
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The first part of the video below illustrates clearly how scientists currently understand DNA compaction. (The second half illustrates DNA replication.) |
Now we unpack this process with some of the detail it deserves.
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[edit] 1. DNA DNA (Deoxyribonucleic acid) contains instructions specifying the biological development of all cellular forms of life, and most viruses. The compaction process described here is related to how DNA is transferred from cell to cell during replication. This packing process can also effect how the genes are coded. |
[edit] 2. Double-helix The DNA double helix typically consists geometrically of two congruent helices with the same axis, differing by a 180 degree translation about the axis. |
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[edit] 3. Nuclear matrix The DNA rests in the nuclear matrix, a network of fibers that may be directly involved in gene expression. |
[edit] 4. Histone  Histones are the proteins that begin the packing process. They begin DNA compaction by binding to the DNA helix, then help give nucleosomess and chromatins their shape, and aid in controlling the activities of genes. |
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[edit] 5. Linker histones Linker histones serve as a ring, which other histones bind to. They are also thought to mediate transcription. They are designated as H1 in the image at right. |
[edit] 6. Nucleosome  Nucleosomes are wheel-like shapes, formed by histone octamer spools that are bound into a circle, around a central ring of H1 histones. |
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[edit] 7. Nucleosomal array The nucleosomal array is an arrangement of condensed nucleosomes. |
[edit] 8. Chromatin Nucleosomal arrays make loops to form chromatin fibers. |
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[edit] 9. Chromatin scaffolding The nuclear scaffold forms rosettes, which in turn form a chromatid. |
[edit] 10. Chromatin scaffolding loops The chromatin scaffolding forms loops. |
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[edit] 11. Chromosomal matrix The chromosomal matrix provides the form of the chromosome. |
[edit] 12. Chromosome The chromosomes in a eukaryotic cell are paired, but are circular and solitary in prokaryotic cells. |
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[edit] 13. Genetic material The genetic material is the collection of chromosomes in a cell. |
[edit] 14. Nucleolus Nucleoli are concentrations of genetic material. |
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[edit] 15. Nucleus The nucleus is the storehouse of a cell's DNA. Many epigenetic processes are mediated by the nucleus. |
[edit] 16. Cell The cell is the basic unit of life. |
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[edit] Etc.[edit] Supercoil |
Follow-up
Now that the parts of DNA compaction have been reviewed, go back and watch the video to see if you can name the components as they begin their work.
See Also
External links
- DNA wrapping -- Excellent YouTube movie illustrating DNA compaction
- Cytographica animations
- Biomolecules Gallery
- Structure Determined for Key Molecular Complex Involved in Long-Term Gene Storage: Genome-Management System Seen as a Natural Protection Against Cancer; Ronen Marmorstein, Wistar Institute
- The Design of DNA Compaction, Cornelius Hunter
