Nucleosome, molecular model. A nucleosome is a subunit of chromatin, the substance that forms chromosomes. It consists of a short length of DNA (deoxyribonucleic acid, red and blue helix) wrapped around a core of eight histone proteins (centre). Here the secondary structure of the proteins is shown. The structure of the nucleosome allows large quantities of DNA, the genetic material, to be packaged into a cell's nucleus.