A nucleosome consists of a cluster of eight histone proteins with a section of DNA wrapping around the outside of them.
Short stretches of DNA join each nucleosome together. These short stretches are known as linker DNA.
The arrangement of nucleosomes joined by linker DNA gives chromatin the appearance of 'beads on a string'.
Sections of chromatin will take on this structure when undergoing transcription. In this formation, transcription factors and RNA polymerase are able to bind to the DNA.