True about nucleosome: (PGI Nov 2009)

Ans: C (Regular repeating structure of DNA & histone proteins) Chromatin is the chromosomal material in the nuclei of cells of eukaryotic organisms:ChromatinQ consists of very long double-stranded DNAQ molecules and a nearly equal mass of rather small basic proteins termed histonesQ as well as a smaller amount of nonhistone proteins (most of which are acidic and larger than histones and a small quantity of RNA.The non histone proteins include enzymes involved in DNA replication and repair, and the proteins involved in RNA synthesis, processing, and transport to the cytoplasm. Histones, is to condense the DNA; however it is important to note that the histones also integrally participate in gene regulation.NucleosomeThe core is composed of two molecules each of histonesQ (H2A, H2B, H3, and H4).Each core with two turns of DNA double helix wrapped around it (approx 150 bp) is termed as nucleosomeQ, the basic unit of chromatin.Electron microscopic studies of chromatin have demonstrated dense spherical particles called nudeosomes, the basic unit of chromatinNucleosomes are separated by linker DNA7 to which h istone; HI is attachedThe continuous string of nucleosome represent beads-on-a - string form of chromatin* "Histones are highly conserved and can he grouped into five major classes: H1/H5. H2A. H2B. H3, and H4". These are organized into two super-classes as follows:core histones - H2A, H2B, H3 and H4linker histones HI and H5# The linker histone H1 binds the nucleosome and the entry 1 and exit sites of the DNA, thus locking the DNA into place I and allowing the formation of higher order structure.Function of histone: to condense DNA7 & to participate in gene regulationQ (Harper 28th/312)