Chromatin

Chromatin is the complex combination of DNA and proteins that makes up chromosomes.Van Holde K.E. 1989. Chromatin. New York: Springer-Verlag. Cooper, Geoffrey M. 2000. The Cell: a molecular approach. 2nd ed, Chapter 4.2 Chromosomes and Chromatin It is found inside the nuclei of eukaryotic cells.

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


 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.

 References 

Category:Chromosomes
Category:Molecular biology