Biochemistry 2280A Study Guide - Final Guide: Histone H1, Atp Hydrolysis, Heterochromatin
9 Feb 2016
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Cell must arrange the dna in a compact form so it can fit within the nucleus. At the same time, dna must be available for transcription. The complex of dna and its organizing proteins is called chromatin. Have many lysine and arginine residues = are positively charged at physiological ph and ideally suited to interact with negatively charged phosphate groups of dna. Dna double helix wraps around 8 histone proteins: two copies each of histone h2a, h2b, h3, h4. Dna makes 1. 7 wraps around the histone core. Nucleosome core particle: the wrapped dna and histone core proteins together. Nucleosome: nucleosome core particle plus the linker together. Compact the dna strand by a factor of three. Nucleosome packs into a coil called a 30nm chromatic fibre. Arrangement of nucleosomes in this fibre favours a zig-zag structure (look at 1st image) In a fibre, the length of the dna has been compacted by a factor of 100.
