Section D Prokaryotic and Eukaryotic Chromosome Structure

1
Section DProkaryotic and Eukaryotic Chromosome
Structure

• D1 Prokaryotic Chromosome Structure
• D2 Chromatin Structure
• D3 Eukaryotic Chromosome Structure
• D4 Genome Complexity
• D5 Central Dogma

2
D1 Prokaryotic Chromosome Structure
If the DNA of E. coli is isolated free of most
attached proteins.
(?Lk/Lk? -0.06).
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.

4
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

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

6
1000nm chromosome section
7
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

8
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.

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.

10
CpG methylation mutation

• CpG methylation mutation
• CpG sites are ? normally methylated and are ?
  relatively scarce throughout most of the genome,
  because 5-methylcytosine
  can spontaneously deaminate to thymine and this
  error is not always repaired.

11
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

12
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)

13
D5 Central Dogma
14

• Thats all for Section D