Nukleosomeja

Nukleosomeja are the fundamental repeating units of chromatin in eukaryotic cells. Each nucleosome consists of a histone protein core around which about 147 base pairs of DNA are wrapped in a left-handed superhelix. The core particle is an octamer of histones: two copies each of H2A, H2B, H3, and H4. The DNA entry and exit points are connected by linker DNA, and a linker histone, H1, binds near the core to promote higher-order compaction.

Nucleosomes package the long eukaryotic genome into a compact, organized structure and regulate access to genetic information. They influence processes such as transcription, replication, and repair by modulating DNA accessibility. The arrangement of nucleosomes along DNA—their positions, density, and post-translational modifications of histone tails—constitutes an epigenetic layer that can alter gene expression without changing the DNA sequence.

Chromatin can be further compacted into higher-order fibers, including the proposed 30-nanometer fiber, though the exact in vivo organization varies among species and cell types. Nucleosome dynamics are controlled by chromatin remodelers, histone chaperones, and post-translational modifications such as acetylation, methylation, and phosphorylation. These features influence how cells respond to developmental cues and environmental signals, and disruptions in nucleosome organization are associated with aging and disease.

Nukleosomeja is the Finnish term for these complexes and corresponds to the concept of nucleosomes used in English-language literature.

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