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Similar DNA packaging exists also in chloroplasts and mitochondria. Bacterial DNA is sometimes referred to as the bacterial chromosome . Bacterial nucleoid evolutionary represents an intermediate engineering solution between the protein-free DNA packing in viruses and protein-determined packing in eukaryotes.
Some alternative forms of DNA packaging [ edit ] The chromatin in mammalian sperm is the most condensed form of eukaryotic DNA, it is packaged by protamines rather than nucleosomes, [ 21 ] whilst prokaryotes package their DNA through supercoiling .
The packaging of eukaryotic DNA into chromatin presents a barrier to all DNA-based processes that require recruitment of enzymes to their sites of action. [31] To allow the critical cellular process of DNA repair, the chromatin must be remodeled.
In contrast to most eukaryotic cells, mature sperm cells largely use protamines to package their genomic DNA, most likely to achieve an even higher packaging ratio. [17] Histone equivalents and a simplified chromatin structure have also been found in Archaea , [ 18 ] suggesting that eukaryotes are not the only organisms that use nucleosomes.
In eukaryotes, DNA is located in the cell nucleus, with small amounts in mitochondria and chloroplasts. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the nucleoid. [97] The genetic information in a genome is held within genes, and the complete set of this information in an organism is called its genotype.
DNA supercoiling is important for DNA packaging within all cells. Because the length of DNA can be thousands of times that of a cell, packaging this genetic material into the cell or nucleus (in eukaryotes) is a difficult feat. Supercoiling of DNA reduces the space and allows for DNA to be packaged.
As architectural DNA components that organize the genome of eukaryotes into functional units within the cell nucleus, S/MARs mediate structural organization of the chromatin within the nucleus. These elements constitute anchor points of the DNA for the chromatin scaffold and serve to organize the chromatin into structural domains.
However, DNA is tightly packaged in the nucleus with the help of packaging proteins, chiefly histone proteins to form repeating units of nucleosomes which further bundle together to form condensed chromatin structure. Such condensed structure occludes many DNA regulatory regions, not allowing them to interact with transcriptional machinery ...