DNA packed into chromatin - histone and nonhistone proteins; repeating unit is nucleosome - DNA wrapped around core of 8 histones. Chromatin maintains structure. Acetylation of histones occurs at ends - plays key role, controlled by histone acetyl transferse (HAT and HDAC). Must become physically accessible/uncoiled for translation - HDAC results in tight coiling. In some cancer cells, an overrecruiment of HDAC resulting in hyper-acetylation and closed chromatin structure.
Why are people in industrialized countries obese? Both mice and people have a gene called agouti. If it is turned on in a mouse, the mouse turns yellow and is obese and prone to diabetes and cancer. When pregnant yellow agouti mothers were fed BPA ( which we get from water bottles and tin cans) more yellow, unhealthy babies were born than normal... [Excellent Article on Epigenetics and Diet]