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Chromatin is a complex of DNA and protein found in eukaryotic cells. [1] The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in reinforcing the DNA during cell division , preventing DNA damage , and regulating gene expression ...
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.
Core histones are found in the nuclei of eukaryotic cells and in most Archaeal phyla, but not in bacteria. [18] The unicellular algae known as dinoflagellates were previously thought to be the only eukaryotes that completely lack histones, [23] but later studies showed that their DNA still encodes histone genes. [24]
Basic units of chromatin structure. Histone H3 is one of the five main histones involved in the structure of chromatin in eukaryotic cells. [1] [2] Featuring a main globular domain and a long N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'beads on a string' structure.
The packaging of DNA into nucleosomes causes a 10 nanometer fibre which may further condense up to 30 nm fibres [33] Most of the euchromatin in interphase nuclei appears to be in the form of 30-nm fibers. [33] Chromatin structure is the more decondensed state, i.e. the 10-nm conformation allows transcription. [33] Heterochromatin vs. euchromatin
Histone H2A is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. The other histone proteins are: H1, H2B, H3 and H4. The crystal structure of the nucleosome core particle consisting of H2A, H2B, H3 and H4 core histones, and DNA. The view is from the top through the superhelical axis.
Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes, this structure involves DNA binding to a complex of small basic proteins called histones. In prokaryotes, multiple types of proteins are involved.
While most histone H1 in the nucleus is bound to chromatin, H1 molecules shuttle between chromatin regions at a fairly high rate. [23] [24]It is difficult to understand how such a dynamic protein could be a structural component of chromatin, but it has been suggested that the steady-state equilibrium within the nucleus still strongly favors association between H1 and chromatin, meaning that ...