Kromatiinan

Kromatiinan (chromatin) refers to the complex of DNA and protein that packages genetic material within the nucleus of eukaryotic cells. It enables the long molecule of DNA to be compacted to fit the nucleus while also regulating access to genetic information.

Chromatin is built from DNA wrapped around histone proteins to form nucleosomes, the basic repeating units. A histone octamer around which about 147 base pairs of DNA are wound forms the nucleosome core; a linker DNA segment and the histone H1 help organize higher-order structure. Histones can incorporate variants, and the tails of histones can be chemically modified, influencing chromatin behavior.

Chromatin exists in different states that correlate with gene activity. Euchromatin is generally less condensed and associated with active transcription, whereas heterochromatin is more condensed and typically transcriptionally silent. The precise arrangement of chromatin is dynamic and is controlled by chromatin remodeling complexes, the pattern of DNA methylation, and post-translational histone modifications such as acetylation and methylation. These epigenetic marks regulate processes including transcription, DNA replication, and repair.

During cell division, chromatin undergoes major condensation to form chromosomes, ensuring accurate segregation. In interphase, its more open configuration permits gene expression and replication. Disruptions in chromatin regulation are linked to developmental disorders and cancer.