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.
Histidine
Asparagine
Aspartate
Glutamate
Molecular Genetics