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Biology ed 2 chromatin beads on a string chromatin

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Unformatted text preview: tes: into chromatin: DNA wound around histone octamer - the nucleosome core core • Histone octamer core: (2X H2a) + (2X H2b) + (2X H3) + (2X H4) (2X • Histone H1: can be Histone removed without affecting nucleosome structure suggesting H1 external to core particle core Acid-urea Acid-urea PAGE for histones histones 18 Weaver 2002 Molecular Biology Ed. 2 CHROMATIN: BEADS ON A STRING CHROMATIN: 30nm fiber Partially unwound 10nm fiber - beads on a string • • lyse nuclei & chromatin fiber released… tightly packed material lyse (30nm fiber) & DNA thread running thru a series of particles (nucleosomes) (nucleosomes) 1 nucleosome = 200bp DNA (includes DNA on & between particles) 19 CHROMATIN: CORE PARTICLE • Micrococcal nuclease releases Micrococcal individual nucleosomes individual • Micrococcal endonuclease Micrococcal cuts DNA between nucleosomes & then digests away linker DNA between particles particles • H1 extracted with moderately H1 low salt low • Nucleosome disk removed Nucleosome from DNA with high salt 20 CHROMATIN: CORE PARTICLE Weaver 2002 Molecular Biology Ed. 2 • Nuclease digestion produces Nuclease core particle of 146bp DNA core wrapped around 4 core histones (H2a, H2b, H3, & H4) histones H3 H4 • DNA follows “tracks” around DNA histone octamer histone 21 CHROMATIN: NUCLEOSOME Weaver 2002 Molecular Biology Ed. 2 • • • • H2A (yellow), H2B (red), H3 (blue), H4 (green) Core histones: histone fold ­ 3 α helices...
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