Kromatín

Kromatín is a complex of DNA and proteins that packages eukaryotic genomes within the nucleus and regulates access to genetic information. It consists largely of DNA wrapped around histone proteins to form nucleosomes—the basic repeating unit of chromatin. A nucleosome core particle contains a histone octamer (two molecules of H2A, H2B, H3, and H4) around which about 147 base pairs of DNA are wound. Linker DNA is associated with histone H1, which helps compact nucleosomes into higher-order structures.

Chromatin exists in dynamic states that influence gene activity. Euchromatin is relatively decondensed and associated with active transcription, while heterochromatin is more condensed and typically transcriptionally silent. The transition between these states is controlled by various mechanisms, including post-translational histone modifications (such as acetylation, methylation, and phosphorylation), DNA methylation, and the activity of chromatin-remodeling complexes that reposition, replace, or eject nucleosomes.

These regulatory layers affect processes such as transcription, DNA replication, and DNA repair. Epigenetic marks can be propagated through cell division, contributing to cell identity without changing the underlying DNA sequence. In addition, non-coding RNAs participate in organizing chromatin structure and function.

Alterations in chromatin structure and epigenetic regulation are linked to development, aging, and diseases, notably cancer. Researchers study chromatin using techniques like ATAC-seq, DNase-seq, ChIP-seq, and Hi-C to assess accessibility, histone modifications, and three-dimensional genome organization.