Eukaryotic chromosome structure
Eukaryotic chromosome structure refers to the levels of packaging from raw
History
The double helix was discovered in 1953 by
Structure
In eukaryotes, such as humans, roughly 3.2 billion nucleotides are spread out over 23 different chromosomes (males have both an X chromosome and a Y chromosome instead of a pair of X chromosomes as seen in females). Each chromosome consists enormously long linear DNA molecule associated with proteins that fold and pack the fine thread of DNA into a more compact structure.[2]
Commonly, many people think the structure of a chromosome is in an "X" shape. But this is only present when the cell divides. Researchers have now been able to model the structure of chromosomes when they are active. This is extremely important because the way that DNA folds up in chromosome structures is linked to the way DNA is used. Scientists have been able to develop the 3D structures of chromosomes in a single cell. The scientists used hundreds of measurements of where different parts of the DNA get close to one another to help create this model. This research was done by scientists at the Department of Biochemistry at Cambridge, working with others from the
Nucleosomes
The
Packaging
Packaging of DNA is facilitated by the electrostatic charge distribution: phosphate groups cause DNA to have a negative charge, whilst the histones are positively charged. Most eukaryotic cells contain histones (with a few exceptions) as well as the kingdom Archaea. Specifically histones H3 and H4 are nearly identical in structure among all eukaryotes, suggesting strict evolutionary conservation of both structure and function.[4] Histones are positively charged molecules as they contain lysine and arginine in larger quantities and DNA is negatively charged. This allows histones to make a strong ionic bond to DNA form a nucleosome. The most basic level of DNA condensation is the wrapping of DNA around the histone core proteins. Higher-order packaging is accomplished by specialized proteins that bind and fold the DNA. This generates a series of loops and coils that provide increasingly higher levels of organization and prevent the DNA from becoming tangled and unmanageable.[4] This complex of DNA and proteins are called chromatin.[5] But in addition to proteins involved with packaging, chromosomes are associated with proteins involved with DNA replication, DNA repair, and gene expression.[6]
References
- ^ "The Francis Crick Papers." : The Discovery of the Double Helix, 1951-1953. N.p., n.d. Web. 16 Nov. 2014.
- ^ "Eukaryotic Chromosome Structure". www.ndsu.edu. Retrieved 15 September 2014.
- ^ "Structure of Chromosomes Revealed." University of Cambridge. N.p., 30 Sept. 2013. Web. 16 Nov. 2014.
- ^ ISBN 978-1-4641-2614-7.)
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: CS1 maint: location missing publisher (link - ^ "Eukaryotic Chromosome Structure". SciencePrimer. Retrieved 15 September 2014.
- ^ "Chromosome". www.nature.com. Retrieved 15 September 2014.