Histonirakenne

Histonirakenne, also known as histone structure, refers to the organization of histone proteins around which DNA is wound in eukaryotic cells. Histones are small, basic proteins that package DNA into structural units called nucleosomes. Each nucleosome consists of approximately 147 base pairs of DNA wrapped around an octamer of histones, which includes two copies each of the histones H2A, H2B, H3, and H4. This compact structure allows for the efficient storage and regulation of genetic information within the cell nucleus.

The histone octamer is composed of two copies of each histone type, forming a complex that resembles a torus. The DNA is wrapped around the histone octamer in a left-handed superhelix, with approximately 1.65 turns of DNA per turn of the histone octamer. The histone proteins are rich in positively charged amino acids, which help to neutralize the negative charge of the DNA, facilitating its condensation into a more compact form.

The histone structure is dynamic and can be modified through various post-translational modifications, such as acetylation, methylation, phosphorylation, and ubiquitination. These modifications can alter the charge and interactions of the histone proteins, influencing DNA accessibility, gene expression, and chromatin remodeling. The histone structure plays a crucial role in gene regulation, DNA replication, and repair, as well as in the maintenance of genomic stability.