生物学专业英语：核小体-细胞周期
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30 nm fiber
300 nm
Nuclear matrix, a protein complex
D2. Chromatin Structure
D3 Eukaryotic Chromosomal Structure
1. Cell cycle 2. mitotic chromosome 3. Interphase chromosomes
Centromere
2. mitotic chromosome
D3 Eukaryotic Chromosomal Structure
2. mitotic chromosome
D2. Chromatin Structure
Nucleosomes and micrococcal nuclease
Micrococcal nuclease: an endonuclease that cleaves naked/nonsupercoiled double-stranded DNA. Treatment of chromatin with micrococcal nuclease led to the isolation of DNA fragments with discrete sizes (~200 bp), the primary structure unit of chromatin termed nucleosome.
Histones: positively charged, rich in lysine and arginie • core histones (H2A, H2B, H3 and H4): 1. 10-20 kDa 2. located in the nucleosome core [octamer core (H2A)2(H2B)2 (H3)2
Nucleosomes : The nucleosome core is the basic unit of
chromosome structure, consisting of a protein octamer containing two each of the core histones, with 146 bp of DNA wrapped 1.8 times in a left-handed fashion around it. The wrapping of DNA into nucleosomes accounts for virtually all of the negative supercoiling in eukaryotic DNA.
(H4)2 3. highly conserved in their sequences • H1 histone: 1. 23 kDa 2. Located outside of nucleosome, bind to DNA more loosely 3. Less conserved in its sequence
D2. Chromatin Structure (ukaryotic cells)
Solving the packing problem: chromatin The length of a chromosome is cm level, but the the diameter
of nucleus is at mm level. The DNA concentration in nucleus is about 200 mg/ml
•Higher ordered •Left-handed helix •Six nucloesomes per turn
Highest level of chromatin organization: looped domain structure
Higher order structure: On the largest scale, chromosomal DNA is organized into loops of up to 100 kb in the form of the 30 nm fiber, constrained by a protein scaffold（蛋白支架）, the nuclear matrix. The overall structure somewhat resembles that of the organizational domains of prokaryotic DNA.
Nucleosome core 146 bp, 1.8 superhelical turn
Chromatosome 166 bp, 2 superhelical turn
The role of H1: A single molecule of H1 stabilizes the DNA at the point at which it enters and leaves the nucleosome core, and organizes the DNA between nucleosomes. A nucleosome core plus H1 is known as a chromatosome. In some cases, H1 is replaced by a variant, H5, which binds more tightly, and is associated with DNA which is inactive in transcription.
D3 Eukaryotic Chromosomal Structure
Cell cycle
D3 Eukaryotic Chromosomal Structure
2. mitotic chromosome
Telomere
The classic picture of paired sister chromatids（姊妹染 色单体）at mitosis represents the most highly condensed state of chromatin. The linear DNA traces a single path from one tip of the chromosome to the other, in successive loops of up to 100 kb of 30 nm fiber anchored to the nuclear matrix in the core.
The role of H1: 1. binds to nucleosome and acts to stabilize the point at which
DNA enters and leaves the nucleosome core. 2. C-terminal tail of H1 larger than the core histones serves to
D3 Eukaryotic Chromosomal Structure
1. Replication occurs during S phase
2. G1 and G2 are intervals to provide additional time for cell growth.
Cell division. A parental cell in G1 has two copies of each chromosome (2n), one maternal (red) and one paternal (blue). Chromosomes are replicated during the S phase, giving a 4n chromosomal complement. At the midpoint of mitosis (metaphase), the replicated chromosomes are aligned and held in position by the mitotic apparatus. The two identical chromatids composing each replicated chromosome then move to opposite ends of the cell, the nuclear membrane re-forms around each set of chromosomes, and finally cytokinesis splits the cell into two genetically identical daughter cells.
Linker DNA <10 to > 100 bp average 55 bp
The 30 nm fiber
The 30 nm fiber: Chromatin is organized into a larger structure, known as the 30 nm fiber or solenoid （螺线管）, thought to consist of a left-handed helix of nucleosomes with appproximately six nucleosomes per helical turn. Most chromatin exists in this form.
Chromatin: The highly ordered DNA-protein complex which makes up the eukayotic chromosomes. >50% of the mass is protein
Chromatin structure also enables the chromosomes to alter their compactness as the cell progress the cell cycle.
Histones : The major protein components of chromatin are the histones; small , basic (positively charged) proteins which bind tightly to DNA. There are four families of core histone, H2A, H2B, H3, H4, and a further family, H1, which has some different properties, and a distinct role. Individual species have a number of variants of the different histone proteins.
stabilize the DNA between the nucleosome cores.
“Beads on a string” structure
Linker DNA: the linker DNA between the nucleosome cores varies between less than 10 and more than 100 bp, but is normally around 55 bp. The nucleosomal repeat unit is hence around 200 bp.
meta phase中期- highly condensed interphase间期- more diffuse Thus, chromatin is the basic organization unit of eukaryotic chromosomal structure
D2. Chromatin Structure
300 nm
Nuclear matrix, a protein complex
D2. Chromatin Structure
D3 Eukaryotic Chromosomal Structure
1. Cell cycle 2. mitotic chromosome 3. Interphase chromosomes
Centromere
2. mitotic chromosome
D3 Eukaryotic Chromosomal Structure
2. mitotic chromosome
D2. Chromatin Structure
Nucleosomes and micrococcal nuclease
Micrococcal nuclease: an endonuclease that cleaves naked/nonsupercoiled double-stranded DNA. Treatment of chromatin with micrococcal nuclease led to the isolation of DNA fragments with discrete sizes (~200 bp), the primary structure unit of chromatin termed nucleosome.
Histones: positively charged, rich in lysine and arginie • core histones (H2A, H2B, H3 and H4): 1. 10-20 kDa 2. located in the nucleosome core [octamer core (H2A)2(H2B)2 (H3)2
Nucleosomes : The nucleosome core is the basic unit of
chromosome structure, consisting of a protein octamer containing two each of the core histones, with 146 bp of DNA wrapped 1.8 times in a left-handed fashion around it. The wrapping of DNA into nucleosomes accounts for virtually all of the negative supercoiling in eukaryotic DNA.
(H4)2 3. highly conserved in their sequences • H1 histone: 1. 23 kDa 2. Located outside of nucleosome, bind to DNA more loosely 3. Less conserved in its sequence
D2. Chromatin Structure (ukaryotic cells)
Solving the packing problem: chromatin The length of a chromosome is cm level, but the the diameter
of nucleus is at mm level. The DNA concentration in nucleus is about 200 mg/ml
•Higher ordered •Left-handed helix •Six nucloesomes per turn
Highest level of chromatin organization: looped domain structure
Higher order structure: On the largest scale, chromosomal DNA is organized into loops of up to 100 kb in the form of the 30 nm fiber, constrained by a protein scaffold（蛋白支架）, the nuclear matrix. The overall structure somewhat resembles that of the organizational domains of prokaryotic DNA.
Nucleosome core 146 bp, 1.8 superhelical turn
Chromatosome 166 bp, 2 superhelical turn
The role of H1: A single molecule of H1 stabilizes the DNA at the point at which it enters and leaves the nucleosome core, and organizes the DNA between nucleosomes. A nucleosome core plus H1 is known as a chromatosome. In some cases, H1 is replaced by a variant, H5, which binds more tightly, and is associated with DNA which is inactive in transcription.
D3 Eukaryotic Chromosomal Structure
Cell cycle
D3 Eukaryotic Chromosomal Structure
2. mitotic chromosome
Telomere
The classic picture of paired sister chromatids（姊妹染 色单体）at mitosis represents the most highly condensed state of chromatin. The linear DNA traces a single path from one tip of the chromosome to the other, in successive loops of up to 100 kb of 30 nm fiber anchored to the nuclear matrix in the core.
The role of H1: 1. binds to nucleosome and acts to stabilize the point at which
DNA enters and leaves the nucleosome core. 2. C-terminal tail of H1 larger than the core histones serves to
D3 Eukaryotic Chromosomal Structure
1. Replication occurs during S phase
2. G1 and G2 are intervals to provide additional time for cell growth.
Cell division. A parental cell in G1 has two copies of each chromosome (2n), one maternal (red) and one paternal (blue). Chromosomes are replicated during the S phase, giving a 4n chromosomal complement. At the midpoint of mitosis (metaphase), the replicated chromosomes are aligned and held in position by the mitotic apparatus. The two identical chromatids composing each replicated chromosome then move to opposite ends of the cell, the nuclear membrane re-forms around each set of chromosomes, and finally cytokinesis splits the cell into two genetically identical daughter cells.
Linker DNA <10 to > 100 bp average 55 bp
The 30 nm fiber
The 30 nm fiber: Chromatin is organized into a larger structure, known as the 30 nm fiber or solenoid （螺线管）, thought to consist of a left-handed helix of nucleosomes with appproximately six nucleosomes per helical turn. Most chromatin exists in this form.
Chromatin: The highly ordered DNA-protein complex which makes up the eukayotic chromosomes. >50% of the mass is protein
Chromatin structure also enables the chromosomes to alter their compactness as the cell progress the cell cycle.
Histones : The major protein components of chromatin are the histones; small , basic (positively charged) proteins which bind tightly to DNA. There are four families of core histone, H2A, H2B, H3, H4, and a further family, H1, which has some different properties, and a distinct role. Individual species have a number of variants of the different histone proteins.
stabilize the DNA between the nucleosome cores.
“Beads on a string” structure
Linker DNA: the linker DNA between the nucleosome cores varies between less than 10 and more than 100 bp, but is normally around 55 bp. The nucleosomal repeat unit is hence around 200 bp.
meta phase中期- highly condensed interphase间期- more diffuse Thus, chromatin is the basic organization unit of eukaryotic chromosomal structure
D2. Chromatin Structure