What is the Difference Between Histones and Nucleosomes?

The main difference between histones and nucleosomes lies in their composition and function:

• Histones are proteins that provide structural support for chromosomes and play a role in regulating gene expression. They are the chief protein component of the chromatin fiber and act as spools around which DNA winds. There are five major families of histone proteins (H1 through H5).
• Nucleosomes are the basic units of DNA packaging and consist of a segment of DNA wound around a core "octamer" of 8 histone proteins (two each of H2A, H2B, H3, and H4). They are the spherical structures formed when positively charged DNA strands are wrapped around a histone octamer. Nucleosomes are connected by H1/H5 linker histones to form a bead-like string of nucleosomes, which make up chromosomes.

In summary, histones are proteins that help organize and compact DNA into chromosomes, while nucleosomes are the structural units formed by the association of DNA with histone proteins. Nucleosomes, in turn, are linked together by linker histones to form chromosomes.

Comparative Table: Histones vs Nucleosomes

Here is a table comparing the main differences between histones and nucleosomes:

In summary, histones are the proteins that DNA is wrapped around, while nucleosomes are the DNA-histone complexes that form the fundamental units of chromosomes. Histones play multiple roles in gene expression, DNA replication, and DNA damage repair, and they can be extensively modified on their N- and C-terminal tails and globular domains. Nucleosomes consist of 147 base pairs of DNA wrapped around an octamer of four core histones, with a histone H1 bound to the linker region between two nucleosomes.