Chromatin Structure in Cell Differentiation, Aging and Cancer

Chromatin is the structure that the eukaryotic genome is packaged into, allowing over a metre of DNA to fit into the small volume of the nucleus. It is composed of DNA and proteins, most of which are histones. This DNA-protein complex is the template for a number of essential cell processes including transcription and replication. The basic structural unit of chromatin is the nucleosome. Nucleosomes comprise around 146 base pairs of DNA wrapped in a left-handed superhelix 1.7 times around a core histone octamer. This 11nm fibre is often referred to as ‘beads on a string’. Chromatin assembly involves wrapping of DNA around histone octameres producing repetitive nucleosomal array followed by folding of chromatin fibre into solenoid-like structure and deposition of non-histone proteins.