Chromatin is a complex of proteins, RNA and DNA that constitutes the physiological state of the genome. Its basic structure is essentially the same in nearly all eukaryotes, from single-celled yeasts to the most complex multicellular organisms (exceptions include the chromatin of dinoflagellates and vertebrate sperm). Its fundamental role is to package the genome in a sufficiently compact form that allows comparatively very large molecules of DNA to fit inside the cell's nucleus. In human cells, the contour length of the DNA molecules comprising the largest chromosomes is nearly 10,000 times the diameter of the nucleus (typically on the order of 5-10 microns). How is this compaction accomplished? Through multiple layers of folding.