Chromatin

Chromatin is the complex combination of DNA and proteins that makes up chromosomes.^[1]^[2] It is found inside the nuclei of eukaryotic cells.

Chromatin is divided into heterochromatin (condensed) and euchromatin (extended) forms.^[3]^[4] Heterochromatin is composed mostly of satellite DNA tandem repeats. The active components of chromatin are DNA and histone proteins, although other proteins also occur.^[5] The functions of chromatin are:

to package DNA into a smaller volume to fit in the cell
to strengthen the DNA to allow mitosis and meiosis
to control DNA replication and gene expression. How this works is not yet clear.

DNA packaging into chromosomes

Chromatin definitions

Simple and concise definition: Chromatin is a macromolecular complex of a DNA macromolecule and protein macromolecules (and RNA). The proteins package and arrange the DNA and control its functions in the cell nucleus.
The DNA + histone = chromatin definition: The DNA double helix in the cell nucleus is packaged by special proteins termed histones. The formed protein/DNA complex is called chromatin. The basic structural unit of chromatin is the nucleosome.

Chromatin Media

Basic units of chromatin structure
the structure of chromatin within a chromosome
The structures of A-, B-, and Z-DNA.
Fig. 2: Alternative structural forms of DNA influencing chromatin structure
A cartoon representation of the nucleosome structure. From PDB 1KX5.
Two proposed structures of the 30 nm chromatin filament. Left: 1 start helix "solenoid" structure. Right: 2 start loose helix structure. Note: the histones are omitted in this diagram - only the DNA is shown.
Four proposed structures of the 30 nm chromatin filament for DNA repeat length per nucleosomes ranging from 177 to 207 bp.Linker DNA in yellow and nucleosomal DNA in pink.
Animated representation of the dynamic formation of chromatin loops through CTCF (red) and condensin rings (yellow)

References

↑ Van Holde K.E. 1989. Chromatin. New York: Springer-Verlag. ISBN 0-387-96694-3
↑ Cooper, Geoffrey M. 2000. The Cell: a molecular approach. 2nd ed, Chapter 4.2 Chromosomes and Chromatin
↑ "Chromatin Network Home Page". Retrieved 2008-11-18.
↑ Dame R.T. (2005). "The role of nucleoid-associated proteins in the organization and compaction of bacterial chromatin". Mol. Microbiol. 56 (4): 858–70. doi:10.1111/j.1365-2958.2005.04598.x. PMID 15853876. S2CID 26965112.
↑ Van Holde K.J. et al 1995. Elements of chromatin structure: histones, nucleosomes, and fibres, p. 1-26. In S.C.R. Elgin (ed) Chromatin structure and gene expression. IRL Press at Oxford University Press, Oxford.

[1] Van Holde K.E. 1989. Chromatin. New York: Springer-Verlag. ISBN 0-387-96694-3

[2] Cooper, Geoffrey M. 2000. The Cell: a molecular approach. 2nd ed, Chapter 4.2 Chromosomes and Chromatin

[3] "Chromatin Network Home Page". Retrieved 2008-11-18.

[4] Dame R.T. (2005). "The role of nucleoid-associated proteins in the organization and compaction of bacterial chromatin". Mol. Microbiol. 56 (4): 858–70. doi:10.1111/j.1365-2958.2005.04598.x. PMID 15853876. S2CID 26965112.

[5] Van Holde K.J. et al 1995. Elements of chromatin structure: histones, nucleosomes, and fibres, p. 1-26. In S.C.R. Elgin (ed) Chromatin structure and gene expression. IRL Press at Oxford University Press, Oxford.

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