Chromosomes condense in three timed chemical waves during cell division, study shows

DNA does not float freely in the cell. Instead, it is wrapped around histone proteins to form structures called nucleosomes. These histones carry numerous chemical modifications that act as molecular signals, controlling how tightly the DNA is packaged and which genes are active. During cell division, this DNA-histone complex—known as chromatin—must be further condensed into compact, rod-shaped chromosomes. Histone modifications play a key role in this process: They change significantly during condensation and regulate the conversion of chromatin.