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Chapter 7. RNA and Chromosome Structure. 13 and 15 September, 2006. Overview. In the cell, DNA is always associated with proteins . In eukaryotes, histones package DNA into chromatin. Proteins serve a structural role, and compact DNA, with regulated access.
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Chapter 7 RNA and Chromosome Structure 13 and 15 September, 2006
Overview • In the cell, DNA is always associated with proteins . • In eukaryotes, histones package DNA into chromatin. • Proteins serve a structural role, and compact DNA, with regulated access. • Chromosomes may be maintained as haploid or diploid. • Gene density is highest in prokaryotes. • Chromosomes replicate in S phase, segregate in M phase. • Nucleosomes are the building blocks of chromosomes.. • Histone H1 stabilizes the 30 nm fiber. • Chromatin structure is highly regulated, often by covalent modification of histones. • Nucleosome positioning is sequence dependent and allows access to transcription factors. • Histone inheritance and assembly is complex, and maintains the modification state of the parent genome. • Nucleosome assembly requires accessory proteins.
H3 and H4 bind the middle and the ends of the DNA, H2A and H2B bind a smaller region.
Histones make nonspecific contacts with the phosphodiester backbone near the minor groove.
Histone H1 binds to linker DNA and stabilizes the 30 nm fiber, which also required N-terminal tails.