井长勤-第十章 细胞核(二)

Little combination with histone H1
Highly acetylated histone
little phosphorylated histone H2B
Rarely variated histone H2A
HMG 14+17 only exist in active chromatin
Constitutive Heterochromatin: Compacted state at all time: Centromere Facultative Heterochromatin:Inactivated at certain phase of life X chromosome inactivation (barr body)
Metaphase chromosome
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2.4.1 nucleosome
The basic unit of chromatin
the lowest level of chromatin organization
10 nm or so The packing ratio of the DNA of nucleosomes is approximately 7:1.
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2.3 Component of chromatin
DNA
histone：H1、H2A、H2B、H3、H4
protein
RNA
nonhistone
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2.3.1 DNA of chromatin
Genetic material in most cells
46 DNA molecules in a human cell, Each DNA molecule forms a linear chromosome
3×109bp / genome The complexity of eukaryotic genomes Genome size generally increases with an organism’s complexity. Nocoding sequence and repeating sequence
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1./yj.asp 2.http://202.116.64.20/wjf/index.htm(中山大学) 3.http://221.10.254.145/204/show.asp?id=49 (川大) 4./ 5./ 6./ 7./ 8./ 9./curriculm
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2.3.1.1 Nonrepeated DNA
Protein-coding sequences
~25-50% of the protein-coding genes are solitary genes. Others belong to gene family, which encode proteins with similar but nonidentical amino acid sequences.
ß -like globin gene family: Contains 5 functional genes
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2.3.1.2 Moderately repeated DNA
Tandemly repeated genes encode rRNAs, tRNAs, and Histones 5S rRNA and pre-rRNA genes: More than 100 copy/Genome. These genes are needed to meet the great cellular demand for their transcripts
H3
H1
H4
Linker DNA
（50-60bp）
H1
H3
H4
DNA：140-160bp、1.75 loop
nucleosome
H2B
H2A
H2A
H4
H2B
H3
histone：H1
Linking t
DNA：50—60bp
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2.4.2 30 nm fiber
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2.4.3 Looped domains
The 30 nm chromatin fiber is gathered into a series of large, supercoiled loops, or domains.
The third level of chromatin organization
The nucleosomal filament is coiled into the higherorder, thicker fiber (30 nm fiber)
The second level of chromatin organization
The DNA-packing ratio is 6-fold.
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Chapter 10 Nuclei and Chromosomes 细胞核和染色体-2
Jing Changqin(井长勤) associate professor E-mail：jingchangqin@
2.2.2 Two classes of heterochromatin
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2.4.1 The structure of nucleosome
Histone core
H3
H2B
10nm
核 小 体
H4
DNA (140-160bp、1.75圈）
histone：2（H2A、H2B、H3、H4）
Core particle
H2A
H2A
H2B
The packing ratio 5:1
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DNA双螺旋
一级结构
二级结构
染色质“串珠”
“螺旋管”
“袢环”
三级结构 超螺旋管
“放射环”
四级结构
中期染色体
In all, DNA is pacted to 1/10000 in length
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The length of DNA is further shortened to one fortieth (1/40).
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2.4.4 Metaphase chromosome
The mitotic chromosome represents the ultimate in chromatin compactness.
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2.5 summary
Nature of chromatin
Two types
Components Organization
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Exercise
1.Explain the key words nucleosome. 2.Tell the differences histone and non-histone. 3.The structure of nucleosome.
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2.3.1.3 Highly repeated DNA
Simple-sequence, Noncoding DNA
Satellite DNA: Centromeres, Telomeres (105~107bp)
Microsatellite DNA:102~105bp at each site
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2.4 Organization of chromatin
Four levels of organization of chromatin
Nucleosome(10 nm in diameter)
30 nm fiber
Looped domains
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Characteristics of active chromatin
active chromatin and inactive chromatin
DNaseⅠ hypersensitive site （超敏感位点）
particularity in biochemistry（生化上具有特殊性）
The most abundant proteins associated with eukaryotic DNA
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2.3.2 Protein of chromatin
Rich in positively charged basic amino acids, which interact with the negtively charged phosphate groups in DNA The amino acid sequences of histones H2A, H2B, H3, H4 are remarkably similar among distantly species
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References and websites
1.翟中和等主编. 细胞生物学，第3版,高等教育出版社， 2007 2.韩贻仁主编. 分子细胞生物学(第3版),高等教育出版 社,2007 3.艾伯茨等著，赵寿元等译. 基础细胞生物学，上海科学技 术出版社，2002 4.王金发. 细胞生物学,科学出版社，2004 5.杨 恬.细胞生物学，人民卫生出版社，2005 6.Karp G. Cell and Molecular Biology,4th ed(2005), 高等教 育出版社,2007 7.Lodish H et al. Molecular Cell Biology. 4th ed. W H Freeman and Company, 2000
Minisatellite DNA:10~100bp at each site
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2.3.2 Protein of chromatin
Histone
Five classes: H1, H2A, H2B, H3, H4
High quantity histone: DNA1:1
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2.3.2 Protein of chromatin
Nonhistone Include a large number of widely diverse structural enzymatic, and regulatory proteins Most of which have to be characterized