BIOL 3P50 Lecture 9: Genome structure, chromatin, and the nucleosome 2
1 Sep 2015
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Document Summary
The nucleosome: building block of a chromosome, core of 8 histone proteins + associated dna. H4: two copies of each form protein core that wraps. Dna of nucleosome: linker histone, h1, binds to linker dna, high content of positively charged amino acids. 20 32% lysine and arginine: small proteins (11 21 kda) Nucleosome assembly: protein core of nucleosome assembles fully only in the presence of dna. Histone tails: core histones each have an amino terminal tail, remain accessible in the assembled nucleosome, not required for association of dna with histone octamer, sites of extensive post-translational modifications that can alter packaging. Heterochromatin vs euchromatin: heterochromatin, condensed chromatin with limited gene expression, constitutive heterochromatin is found at telomeres and centromeres. & is important for their function: usually repetitive sequence, always forms heterochromatin, facultative heterochromatin refers to heterochromatin that can also exist in a euchromatic state, euchromatin, more loosely packed, open structure, higher levels of gene expression.
