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Chapter 13 Chromatin Structure and Its Effects on Transcription
13.1 Histones(组蛋白) / Eukaryotic cells contain 5 kinds of histones -H1 -H2A H2B H1 -H3 H3 -H4 H2B H2A √ Each histone type isn't H4 homogenous(同质的) -Gene reiteration(重复) -Posttranslational modification 13-2
13-2 13.1 Histones (组蛋白) ✓ Eukaryotic cells contain 5 kinds of histones – H1 – H2A – H2B – H3 – H4 ✓ Each histone type isn’t homogenous (同质的) – Gene reiteration (重复) – Posttranslational modification
Properties of Histones Abundant proteins whose mass in nuclei nearly equals that of dNA Pronounced positive charge at neutral pH Most are well-conserved from one species to another Not single copy genes,repeated many times -Some copies are identical -Others are quite different -H4 has only had 2 variants ever reported 13-3
13-3 Properties of Histones ✓ Abundant proteins whose mass in nuclei nearly equals that of DNA ✓ Pronounced positive charge at neutral pH ✓ Most are well-conserved from one species to another ✓ Not single copy genes, repeated many times – Some copies are identical – Others are quite different – H4 has only had 2 variants ever reported
13.2 Nucleosomes(核小体) Chromosomes are long,thin molecules that will tangle(混乱状态)if not carefully folded Folding occurs in several ways First order of folding is the nucleosome -X-ray diffraction(衍射)has shown strong repeats of structure at 100A intervals -This spacing approximates the nucleosome spaced at 110A intervals 13-4
13-4 13.2 Nucleosomes (核小体) ✓ Chromosomes are long, thin molecules that will tangle (混乱状态) if not carefully folded ✓ Folding occurs in several ways ✓ First order of folding is the nucleosome – X-ray diffraction (衍射) has shown strong repeats of structure at 100Å intervals – This spacing approximates the nucleosome spaced at 110Å intervals
Histones in the Nucleosome Chemical cross-linking in solution: -tetramer(H3-H4)2 - H2A-H2B dimer √Chromatin(染色质)is composed of roughly equal masses of DNA and histones Corresponds to 1 histone octamer per 200 bp of DNA -Octamer composed of: ·2 each H2A,H2B,H3,H4 (H3-H4)2 ·NoH1 Two H2A-H2B dimer 13-5
13-5 Histones in the Nucleosome ✓ Chemical cross-linking in solution: – tetramer (H3-H4)2 – H2A-H2B dimer ✓ Chromatin (染色质) is composed of roughly equal masses of DNA and histones – Corresponds to 1 histone octamer per 200 bp of DNA – Octamer composed of: • 2 each H2A, H2B, H3, H4 • No H1 (H3-H4)2 Two H2A-H2B dimer