mol12 - BIMM100: Lecture 12 continuing Chapter 6 Nature...

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BIMM100: Lecture 12 continuing Chapter 6 Chromatin and Chromosomes Still don’t have your midterm? Pick up exams from K. McPherson 3100E Pac Hall, 8-11 M-F New techniques: – DNase I digestion as a probe for chromatin structure (Fig 6-32) – Chromosome ‘painting’ to evaluate whole genomes (p. 215; 258) Nature Genetics , May 2009
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DNA packaging Spatial problem: How do you fit 6x10 9 bps of DNA in a single human cell? • the human genome (linearized) would be over 6 ft long • average cell nucleus diameter is 6 µ m • packaged DNA in an organized fashion • DNA must be readily accessible for replication, repair, and transcription Solution: DNA in the context of chromatin
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MCB 6-1 DNA organization in eukaryotic cells • histones and the nucleosome (beads on a string) –histone modifications –heterochromatin vs. euchromatin • loops of 30-nm fibers • higher-order chromatin structure 1 2 3 4 5
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What is chromatin? DNA + proteins (about half of each) “beads on a string” 30-nm fiber MCB 6-28 low salt physiological salt • basic structural unit of chromatin • DNA + histones • DNA is wound 1 2 / 3 times around histone core • 147 bps per nucleosome • linkers vary in length (10-90 bps) nucleosomes histone core DNA
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Histones majority of protein in chromatin small but abundant proteins contain many positively charged amino acids core histones are highly conserved gene families (multiple copies in genome)
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5 histone types • H1 (linker) • H2A, H2B, H3, H4 (core) MCB 6-31a Histones and the nucleosome H3/H4 dimer tetramer H2A/H2B dimer tetramer octameric histone core + DNA H1 + + nucleosome
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Histone modifications MCB 6-31b • methylation (R, K) • acetylation (K) • ubiquitination (K)
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mol12 - BIMM100: Lecture 12 continuing Chapter 6 Nature...

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