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Section D Prokaryotic and Eukaryotic Chromosome Structure

Section D Prokaryotic and Eukaryotic Chromosome Structure. D1 Prokaryotic Chromosome Structure D2 Chromatin Structure D3 Eukaryotic Chromosome Structure D4 Genome Complexity D5 Central Dogma. Supercoiling. 50~100kb Domain. broken in one strand. D1 Prokaryotic Chromosome Structure.

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Section D Prokaryotic and Eukaryotic Chromosome Structure

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  1. Section DProkaryotic and Eukaryotic Chromosome Structure D1 Prokaryotic Chromosome Structure D2 Chromatin Structure D3 Eukaryotic Chromosome Structure D4 Genome Complexity D5 Central Dogma Yang Xu, College of Life Sciences

  2. Supercoiling 50~100kb Domain broken in one strand D1 Prokaryotic Chromosome Structure If the DNA of E. coli is isolated free of most attached proteins. (Lk/Lk = -0.06). Yang Xu, College of Life Sciences

  3. The Escherichia coli Chromosome • Prokaryotic genomes are exemplified by the E. coli chromosome. • The DNA in E. coli cells consists of: • a single closed-circular DNA molecule • it is of length 4.6 million base pairs. • The DNA is packaged into nucleoid region: • this region has a very high DNA concentration, perhaps 30-50 mg/ml, (a fairly high DNA concentration in the test tube would be 1 mg/ml). • this region contains all the proteins associated with DNA, such as: polymerases, repressers. • In normal growth, the DNA is being replicated continuously. Yang Xu, College of Life Sciences

  4. 30nm 300 nm loops nuclear matrix D2 Chromatin Structure • Chromatin: Nucleoprotein complex • Histones: H2A, H2B, H3 and H4 + H1 • Nucleosome: Nucleosome/core • The role of H1: Stabilize • Linker DNA: 55 bp • 30 nm fiber: Six per turn/left-handed helix • Higher order structure DNA core 146bp H1 Nucleosome 166bp Yang Xu, College of Life Sciences

  5. D2 Chromatin Structure • Chromatin : Nucleoprotein complex • Nucleosome : Nucleosome/core • Histones: Histone octamer + H1 • Linker DNA: 55 bp • 30 nm fiber: Six per turn/left-handed helix • Higher order structure Yang Xu, College of Life Sciences

  6. Core histones: H2A, H2B, H3 and H4+146 bp of DNA Nucleosome core H1+ 20 bp of DNA Chromatosome 55 bp of linker DNA 200 bp Nucleosomal repeat unit 30 nm fiber 300nm loops 1000nm chromosome section Yang Xu, College of Life Sciences

  7. 1 m m Telomeres centromere 300nm 30nm D3 Eukaryotic Chromosome Structure • The mitotic chromosome • The centromere • Telomeres • Interphase chromosomes • being transcribed • cannot be visualized • Heterochromatin • transcriptionally inactive region • Euchromatin • transcriptionally active region Yang Xu, College of Life Sciences

  8. Short regions Longer regions Loop DNase I hypersensitivity DNase I is an enzyme that cuts the backbone of DNA unless the DNA is protected by protein. DNase I hypersensitivity has been used to map the regions of trans-criptionally active chromatin: • Short regions: the naked DNA can be attacked by DNase I. • Longer regions: where transcription is taking place. These regions vary between different cell types and different phases during cell development. Yang Xu, College of Life Sciences

  9. CpG methylation • Definition: It is the methylation of C-5 in the cytosine base of 5'-CG-3' sequences in mammalian cells. • Function: It is an important chemical modification which is involved in keeping the appropriate level of chromosomal packing at the sites of expressed genes. Yang Xu, College of Life Sciences

  10. CpG methylation mutation • CpG methylation mutation: CpG sites are ① normally methylated and are ② relatively scarce throughout most of the genome, because 5-methylcytosine can spontaneously deaminate to thymine and this error is not always repaired. Yang Xu, College of Life Sciences

  11. Short regions Longer regions Loop methylated 2 kb 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 CpG island housekeeping genes Yang Xu, College of Life Sciences

  12. E. coli (1) (2) (3) 1.0 F of ssDNA (Cot) D4 Genome Complexity • Non-coding DNA interspersed repeated DNA tandemly repeated DNA • Reassociation kinetics Step 1: broken by sonication into same size Step 2: DNA fragments are thermally denatured Step 3: re-anneal at a low concentration Step4: 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) Yang Xu, College of Life Sciences

  13. D5 Central Dogma Yang Xu, College of Life Sciences

  14. That’s all for Section D Yang Xu, College of Life Sciences

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