True about nucleosome:
C i.e. Regular repeating structure of DNA & histone proteins- Histones are small basic proteins rich in basic aminoacid arginine & histidine with alkaline isoelectric pH. It is a simple proteinQ ie its complete hydrolysis only yields amino acids. They are soluble in water, salt solution & diluteacids but not in ammonia and do not easily coagulate on heating. Histones are synthesized in cytoplasm and migrate to nucleus to form conjugated nucleoprotein (chromatin) with nucleic acid (DNA)Q. Histones act as repressor of template activity of DNA in RNA synthesis. Histones also conjugate with porphyrins. Globin, the protein pa of hemoglobin is an atypical histone and it has predominance of histidine & lysine instead of arginine.- Nucleosome, the fundamental organizational units of chromatin (chromosome), consists of regular repeating "beads on a string" arrangement in which histone octamer i.e. (H3 -H4)2 - (H2A - H2B)2 forms the core (bead) around which 146 base pair double stranded DNA is wrapped and 30 bp/54 bp linker DNA and H1 histone protein forms string.- Histone acetylation (by histone acetyl transferase = HAT) causes increased (trancriptionally active) relatively uncondensed euchromatin formation(2. Acetylation or phosphorylation of lysine residue at aminoterminal decreases positive (+) charge of basic histone protein, there by decreasing their association with negatively charged DNA, thus releasing nucleosomes and allowing access to DNA. Histone deacetylation (by histone deacetylase = HDAC) removes acetyl group, restores positive charge and causes increased formation of transcriptionally inactive hetero chromatin (relatively condensed).- Histone is post translationally modified by ribosylation, ubiquitin binding, phosphorylation, acetylation and methylation (RUPAM).
Use only one type of histone protein
Each complex is separated from each other by non histone proteins
Regular repeating structure of DNA & histone proteins
Reflect small nucleus