Yeast Chromatin

In human and other eukaryotic cells, the DNA does not exist as a naked molecule. Instead, it is tightly associated with various proteins in a structure known as chromatin; a term first coined by the German biologist Walther Flemming in 1881. The fundamental sub unit of chromatin is the nucleosome which consists of approximately 146 base-pairs of DNA wrapped around an octamer of histone proteins (two each of histones H3, H4, H2A and H2B). At the most basic level, these nucleosomes are positioned at intervals along the DNA to form a ‘beads on a string’ structure. This structure can then fold up on itself to form higher order structures to ultimately package the DNA so that the genome can fit inside the cell nucleus.