| In diploid eukaryotic cells, the chromatin fibers are about 20nM in diameter. They consist of two major components in equal amounts, DNA and basic proteins called histones. Histones are believed to be regularly arranged in the deep groove of the DNA helix. The recurring positive charges of the histones form electrostatic associations with the negatively charged phosphate groups of DNA, making the DNA more stable and flexible. This allows for the supercoiling of the chromatin fibers. Histones are basic nuclear proteins that are responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. Nucleosomes consist of approximately 146 bp of DNA wrapped around a histone octamer composed of pairs of each of the four core histones (H2A, H2B, H3, and H4). The chromatin fiber is further compacted through the interaction of a linker histone, H1, with the DNA between the nucleosomes to form higher order chromatin structures. Linker histones are involved in the formation of higher order structure in chromatin and the maintenance of overall chromatin compaction. Whilst the core histones are highly conserved across a wide range of organisms, the linker histones are less conserved. |
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