Eukaryotic chromosome structure
- Eukaryotic chromosome structure
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Eukaryotic chromosome structure refers to the levels of packaging from the raw DNA molecules to the chromosomal structures seen during metaphase in mitosis or meiosis.
Structure
In eukaryotes the chromosomes are found packaged within a nuclear membrane, unlike the case in prokaryotes. This membrane consists of a DNA double helix bound to an octamer of core histones (2 dimers of H2A and H2B, and an H3/H4 tetramer). Together, the DNA bound around this histone core forms what is known as the nucleosome. 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 (~0-100 bp) separate the nucleosomes.
Packaging of DNA is facilitated by the electrostatic charge distribution: phosphate groups cause DNA to have a negative charge, whilst the histones are positively charged. Most eukaryotic cells contain histones (with a few exceptions) as well as the kingdom Archaea, a protist group. Histones are positively charged molecules as they contain lysine and arginine in larger quantities and DNA is neatively charged. So they make a strong ionic bond in between them to form nucleosome.
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