noun, plural: nucleosomes
A nucleosome is any of the repeating units of organisation of chromatin. It consists of around 200 base pairs and two molecules each of the histones H2A, H2B, H3 and H4. Most of the DNA (around 140 base pairs) is believed to be wound around a core formed by the histones, the remainder joins adjacent nucleosomes, thus forming a structure reminiscent of a string of beads. The nucleosome core particle is one in which there is about 146 bp of DNA around the histone octamer. The adjacent nucleosome core particles are joined by a stretch of DNA segment called linker DNA. The linker DNA consists of about 10 to 80 bp. Forming nucleosomes is essential to pack a large genome into the nucleus. Without histone cores from where the DNA wounds around, the genome would be too lengthy to fit into the nucleus, which roughly has about a diameter of 10 µm. Nucleosomes were first observed by Don and Ada Olins in 1974 and their structure was described by Roger Kornberg.
- nu body