Proteins in nucleosome are made up of -

Ans. is 'a' i.e., Histidine* Histones are positively charged by virtue of their composition. They are made up of positively charged or basic aminoacids - Histidine and Arginine* Human chromosome when fully extended will measure a few metres long* Such a long chromosome is packed inside a nucleus of few microns in diameter* This is made possible by histones* Histones are basic proteins - in the sense that they are positively charged. They are made up of lysine and arginine (basic aminoacids)* DNA is negatively charged* So there is an electrostatic attraction between positively charged histones and negatively charged DNA and a segment of double stranded DNA(dsDNA) gets wrapped around histone. This gives the first level of compactness. Hence DNA is amphipathic, i.e., it contains both polar and non polar regions.* There are five types of histones. HI, H2A, H2B, H3. H4.* Of these all except HI, the remaining four form dimers to form a histone octamer. This histone octamer sits in the centre and that is surrounded by a segment of dsDNA of length approx. 146 bp (in a left handed supercoiling). This string on bead appearance is called as nucleosome (FIG).* Several such nucleosomes exist, which are connected by a linker fragment. (Imagine you having a string on which you have placed multiple beads at various places and you have allowed the string to wind around the beads) HI histone is found in the linker fragment.