Chromatin contains all of the DNA within the cell nucleus. Small amounts of a special DNA are also found in the mitochondria outside of the cell nucleus. The role of DNA in the cell economy is that of a library of blueprints for RNA, protein, and further DNA synthesis. One of the strictest parameters of chromatin function is that of the fidelity of copying the original DNA template into the RNA, protein, and DNA copies. Miscopying can result in non-functioning products. Another parameter is that of the repair of DNA damage or of point mutations. Persistent DNA damage can also result in non-functioning products.

Beyond the fidelity of copying and the repair of damage, epigenetic mechanisms involving RNA, protein, lipid, hormone and vitamin signals select specific gene loci for transcription to RNA and proteins. Loss of such signals from other genes or from the cell exterior results in a decreased production of RNA and protein specific for the particular gene locus. Excessive or inappropriate signalling may result in abnormal gene expression, as in the re-appearence of fetal RNA and protein species in adult neoplasms or during regeneration of adult organs.

Chromatin functions such as copying, repair, transcription and replication can be viewed in the conventional format of enzyme reactions, with assays of reactant and product concentrations, enyme specific activity and reaction rates, and effects of reaction inhibitors and promoters.

Chromatin functions can also be viewed in a more global context as flows of genetic and epigenetic information, from the DNA library, from hormones and vitamins outside the cell, and from RNA and protein molecules inherited from the dividing mother cell at the time of mitosis. Such information flows also have their concentrations of input and output, their capacity for integrative transformations, and their resistances to such transformations and output, as do conventional enzyme reactions.

1. Frenster JH, "Mechanisms of Repression and De-Repression within Interphase Chromatin", in: "The Chromosome: Structural and Functional Aspects", Dawe CJ, and Yerganian G, (eds.), In-Situ, vol. 1, pp. 78-101, (June, 1965). 

euchromatin: "the most active portion of the genome within the cell nucleus".