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The nucleosome is the fundamental subunit of chromatin. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4.
The nucleosome assembles when DNA wraps around the histone octamer, two H2A-H2B dimers bound to an H3-H4 tetramer. The nucleosome core particle is the most basic form of DNA compaction in eukaryotes. Nucleosomes consist of a histone octamer surrounded by 146 base pairs of DNA wrapped in a superhelical manner. [10]
The generally accepted parts of modern cell theory include: All known living things are made up of one or more cells [13] All living cells arise from pre-existing cells by division. The cell is the fundamental unit of structure and function in all living organisms. [14] The activity of an organism depends on the total activity of independent ...
However, in order for the cell to function, proteins must be able to access the sequence information contained within the DNA, in spite of its tightly-packed nature. Hence, the cell has a number of mechanisms in place to control how DNA is organized. [4] Moreover, nuclear organization can play a role in establishing cell identity.
In eukaryotic cells, DNA is associated with about an equal mass of histone proteins in a highly condensed nucleoprotein complex called chromatin. [14] Deoxyribonucleoproteins in this kind of complex interact to generate a multiprotein regulatory complex in which the intervening DNA is looped or wound.
The nucleosome is the basic unit of DNA condensation and consists of a DNA double helix bound to an octamer of core histones (2 dimers of H2A and H2B, and an H3/H4 tetramer). About 147 base pairs of DNA coil around 1 octamer, and ~20 base pairs are sequestered by the addition of the linker histone (H1), and various length of "linker" DNA (~0 ...
The nucleoplasm, also known as karyoplasm, [1] is the type of protoplasm that makes up the cell nucleus, the most prominent organelle of the eukaryotic cell. It is enclosed by the nuclear envelope , also known as the nuclear membrane. [ 2 ]
The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes. Each human cell contains roughly two meters of DNA. [1]: 405 During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the ...