Can you imagine that if we extend and align our DNA end by end, it will be long enough to go across the middle of the Africa. Yes, it is true.
Our DNA is packed in the unit called nucleosome. The scaffold of the nucleosome is consisted of a series of proteins called histones. Different histones including H2A, H2B, H3 and H4 bind to each other to form a round octamer. 147 nucleorides are twisting around this histone complex. Together with linker nucleorides between histone complexes, about 200 nucleorides are contained in one nucleosome. Nucleosomes then further wind along the same axis to form a nucleosome fiber, standing vertically relative to the fiber axis. N terminals of histone subunits are critical for this fiber forming and covalent modification can be made on N terminals to activate or deactivate a certain DNA region.
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