Chromosomal proteins are the histones around which the DNA strands are coiled to form nucleosome complex which is a small unit of the chromatin.

The first level of organization, or packing, is the winding of DNA strands around histone proteins. Histones package and order DNA into 30nm structural units called nucleosome complexes, which can control the access of proteins (like enzymes) to the DNA regions. Many nucleosomes join together to form chromatin that is present inside the chromosome.

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Key Points

• DNA is packaged by wrapping around histone proteins into structures called nucleosomes, which resemble beads on a string.

• Nucleosomes are small units of chromatin that is present inside the chromosome.

Key Terms

nucleosome: any of the subunits that repeat in chromatin; a coil of DNA surrounding a histone core

histone: any of various simple water-soluble proteins that are rich in the basic amino acids lysine and arginine and are complexed with DNA in the nucleosomes of eukaryotic chromatin

chromatin: the structure formed of DNA and protein present inside a chromosome

chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes