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12 Cards in this Set
- Front
- Back
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what is used to separate individual nucleosomes? |
it can be seperated out by limited digestion of chromatin with micrococcal nuclease followed by seperation of the particles on sucrose gradients |
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what are the core histone proteins |
H2A, H2B, H3, H4 |
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are histones basic or acidic |
basic |
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how are histones solublised from chromatin |
by dilute acids ( 1M 10% acetic acid) |
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which residues are histones rich in |
positively charged arginine and lysine |
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describe the 4 types of interactions between histones and DNA |
1. electrostatic interactions -helix dipoles from alpha-helices in H2B, H3 and H4 cause a net positive charge to accumulate at the point of interaction with negatively charged phosphates of DNA 2. H bonds - between the amine group on the main chain of histone proteins and DNA backbone 3. non-polar interactions - between histone and deoxyribose on DNA 4. salt links and H bonds - between side chains of basic arginine and lysine and phosphate oxygens on DNA |
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what are the 2 levels of organisation of the chromatin |
1. solenoid fibre (30nm) - heterochromatin 2. beads on strong (11nm) - euchromatin |
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describe is the 1st level of organisation of the chromatin |
11nm fibril -147bp DNA wrapped around a basic histone protein (1.67 turns) -adjacent nucleosomes joined by linker/spacer DNA of 50 bp -11nm fibril results in 6 fold reduction in total length -invariant component of both euchromatin and heterochromatin -transcriptionally active form of chromatin |
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describe the second level of organisation of the chromatin |
30nm fibril -forms a left-handed solenoid fibre with 6 nucleosomes per turn -results in 40 fold reduction in total length -H1 histone required for this condensation -inactive in RNA synthesis |
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describe the 3rd level of organisation of the chromatin |
Loops, rosettes and coils - loops - 75kb DNA -rosettes - 6 loops -coils - 30 rosettes -10,000 fold reduction in heterochromatin -no rosettes in euchromatin -scaffold attachment regions required |
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describe the 4th level of organisation |
chromatids -chromatin maximally condensed in mitosis -having a packing ratio of more than 10,000 -5 micrometres long |
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what is the chromosome nuclear scaffold |
-scaffold is a network of proteins that cross-tie the DNA loops -topoisomerase 2 and SC2 (XCAP C/E) are major components -both required for chromosome assembly -these proteins bind to the scaffold attachment regions on the chromosomal DNA -SAR regions rich in AT DNA -SARs define the basis of DNA loops -SARs participate in chromosome assembly and structural maintenance. |
