基因 Chapter 29 Nucleosomes.pdf

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2017-10-16 发布于江西
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基因 Chapter 29 Nucleosomes.pdf

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Nucleosomes CHAPTER OUTLINE Introduction The Path of Nucleosomes in the Chromatin Fiber The Nucleosome Is the Subunit of All Chromatin • 10 nm chromatin fibers are unfolded from 30 nm fibers and consist of a string of nucleosomes. • Micrococcal nuclease releases individual nucleosomes from chromatin as 11S particles. • 30 nm fibers have six nucleosomes/turn, which are orga nized into a solenoid. • A nucleosome contains -200 bp of DNA, two copies of each core histone (H2A, H2B, H3, and H4). • Histone H1 is required for formation of the 30 nm fiber. • DNA is wrapped around the outside surface of the protein Reproduction of Chromatin Requires Assembly octamer. of Nucleosomes DNA Is Coiled in Arrays of Nucleosomes • Histone octamers are not conserved during replication, but H2A-H2B dimers and H3z-H42 tetramers are conserved . • 95% of the DNA is recovered in nucleosomes or multimers when micrococcal nuclease cleaves DNA of chromatin. • There are different pathways for the assembly of nucleo • The length of DNA per nucl