How are the following formed and involved in DNA packaging in a nucleus of a cell? (a) Histone octamer (b) Nucleosome (c) Chromatin
Packaging of DNA. (a) Histone octamer: Five types of histone proteins (H1, H2A, H2B, H3, and H4) are involved. Out of these, four of them H1 A, H2 B, H3, and H4 occur in pairs to produce histone octamer also called the nu body. Histones are organized in a form of a compact unit formed of 8 molecules hence called histone octamer. (b) Nucleosome: The unit of compaction of DNA is the nucleosome. About 146 bp of DMA is wrapped over histone octamer for 1 34 turn to form nucleosome of the size 110 × 60 A. (c) Chromatin: Linker DNA connects two adjacent nucleosomes. It bears H1 protein. As a result, a chain is formed called chromatic. Nucleosome chain gives ‘beads on string’ appearance under the electron microscope. Chromatin are repeating units of a structure located on the nucleosome.
