Chromatin

Definition

Chromatin is the structure in which the DNA, i.e. the genetic information, is packed. Chromatin consists on the one hand of DNA and on the other hand of various proteins. The function of chromatin is the tight packaging of the DNA.

This packaging is necessary because the DNA as such would be much too long to fit into the cell nucleus. Chromatin can exist in different forms. On the one hand, the proteins involved cause the DNA to roll up around proteins called histones. In addition, so-called non-histone proteins cause further compression of the chromatin.

How is chromatin structured?

The smallest unit of chromatin is the complex of DNA and DNA-binding proteins. Despite the high compression of the DNA, it can be read. However, the chromatin is not homogeneously structured.

There are parts of the chromatin that are more dense. In this so-called heterochromatin there are sections of the DNA that cannot be read. The sections that are less dense are called euchromatin.

Here there are sections that are read off. However, some sections of the heterochromatin can be activated. This property is used for genes that do not need to be read off permanently.

Epigenetics describes these properties of chromatin, the activity of the individual gene sections can vary. Various mechanisms can be used to loosen or compress the chromatin. The chromatin structure results from the interaction of DNA, histones and non-histone proteins.

The lowest level of the chromatin structure is the pure DNA chain. The next stage is the combination of DNA and histones. The resulting structure can be imagined like a string of pearls.

The DNA is wrapped around histones, which in turn are arranged in a cord-shaped structure. The combination of DNA and histone is also called nucleosome. The next stage of the chromatin structure is achieved by a denser packaging of the individual nucleosomes.

The resulting structure thus becomes shorter and wider. This structure then forms the superordinate structure of the chromatin through further condensation. The resulting structure is the chromosome. This topic could also be of interest to you: Nuclear division

What is the function of chromatin?

When looking at the functions of chromatin, it is necessary to distinguish between the DNA and protein parts. The function of the DNA part is to store genetic information. The sense of the genetic information is that the DNA is read in different steps, and in the last step a protein is built from this “building template”.

The function of the proteins contained in chromatin is the packaging of the DNA. On the one hand, the packaging ensures that the DNA fits into the cell nucleus. The protein part of the chromatin can also be distinguished between different proteins.

The histones are proteins that bind the DNA to themselves by their charge. One can imagine the histones as small cable drums around which the DNA is wrapped. The other proteins of chromatin are called non-histone proteins. These in turn interact with the DNA and the histones, thereby further compressing the DNA. This topic might also be interesting for you: Tasks of the cell nucleus