Section D: Chromosome Structure Yang Xu, College of Life Sciences Section D Prokaryotic and Eukaryotic Chromosome Structure D1 Prokaryotic Chromosome Structure D2 Chromatin Structure D3 Eukaryotic Chromosome Structure D4 Genome Complexity D5 Central Dogma
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Section D: Chromosome Structure Yang Xu, College of Life Sciences
CpG sites are normally methylated and are relatively ① ②scarce throughout most of the genome, because 5-methylcytosine can spontaneously deaminate to thymine and this error is not always repaired.
Section D: Chromosome Structure Yang Xu, College of Life Sciences
CpG island
• CpG island: where the proportion of CG dinucleotides is much higher than on average
– The CpG there is unmethylated, – These islands are commonly around 2000 bp long, and
may be largely free of nucleosomes,– and are coincident with regions of particular sensitivity to
DNase I.• Function of CpG island: The CpG islands surround the
promoter regions of housekeeping genes
2 kb
CpG island
housekeeping genes
methylated
Shortregions
Longerregions
Loop
Section D: Chromosome Structure Yang Xu, College of Life Sciences
D4 Genome Complexity
• Non-coding DNAinterspersed repeated DNAtandemly repeated DNA
• Reassociation kineticsStep 1: broken by sonication into same size Step 2: DNA fragments are thermally denaturedStep 3: re-anneal at a low concentrationStep4: by spectroscopic analysis
• Satellite DNA: are found in phase (1)• Dispersed repetitive DNA: Alu, L1 (2)• Tandem gene clusters: rDNA and histone genes (2) • Unique sequence DNA is found in (3)
F of ssDNA
1.0
(Cot)
(1)
(2)
(3)
E. coli
Section D: Chromosome Structure Yang Xu, College of Life Sciences
D5 Central Dogma
Section D: Chromosome Structure Yang Xu, College of Life Sciences