Initially, DNA wraps around histone proteins to form nucleosomes, which are the basic repeating units of chromatin. These nucleosomes consist of approximately 146 base pairs of DNA wrapped around a histone octamer composed of two copies each of histone proteins H2A, H2B, H3, and H4. Multiple nucleosomes are then connected by linker DNA and linker histones to form a structure that resembles beads on a string. This structure undergoes further compaction and folding to generate higher-order chromatin fibers, which can be further condensed into chromosomes during cell division.
Chromatin fibers are then able to unwind when DNA replication or transcription occurs, allowing access to the genetic information encoded in the DNA strands. The assembly of DNA into chromatin structure is crucial for packaging DNA within the nucleus, regulating gene expression, and maintaining genomic stability.