CBSE Class 9 Answered

Chromatin is the complex continuum of DNA and proteins, packaged together to form the genetic material of the chromosomes. The chromatin is organized in several progressive levels of organizational complexity, which coils the DNA into more and more compact forms through combination of histone proteins, while still ensuring that it remains accessible.

The basic coiled unit of chromatin is a nucleosome, which consists of a single loop of DNA material wrapped around a histone protein. These nucleosomes are then coiled into an even more complex form and organized into 30 nanometer chromatin fibers. These fibers have nucleosome arrays arranged in 'beads-on-string' fashion. Then these fibers are further coiled to form the chromosomes. The chromatin structure gets modified during various phases of cell division, to make the genetic code more accessible and readable. These modifications in structure are made possible due to changes in histone proteins, which are the building blocks of DNA structure.

The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene expression and DNA replication.