Basic Groups of Microbes

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Basic Groups of Microbes

• Eubacteria
• E. coli Salmonella typhimurium
• Archaea
• Thermophiles
• Eukaryotes
• Fungi
• Protozoa
• Algae

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Diverse Microbes
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Molecular Biology of Microorganisms

• Fundamental principles
• Important functions
• Nitrogen cycle
• Carbon cycle
• Detoxification
• Pathogenic bacteria
• http//vm.cfsan.fda.gov/7Emow/intro.html
• Anti-biotic resistance
• Biotechnology
• Engineering specific proteins
• Biomedical research

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Advantages of Microbes

• Short life-cycle
• Doubling time of E. coli is about 20 min.
• Haploid
• Only have one copy of each gene
• Diverse living environments
• Evolution studies
• Commercially valuable bio-products

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Central Dogma

• DNA

Replication
Transcription
Reverse Transcription
RNA
Translation
Protein
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Replication
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Transcription
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Translation
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Reverse Transcription
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Genetics vs. Biochemistry

• Create mutants
• Genotypes
• Gene function

• Purify proteins
• Phenotypes
• Protein function

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DNA Replication

• A fundamental process
• Experimentally demonstrated

DNA
DNA
DNA
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DNA Replication
THREE HYPOTHESES FOR DNA REPLICATION
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SEPARATION OF DNAS BY CESIUM CHLORIDE DENSITY
GRADIENT CENTRIFUGATION (a) Photo of DNA in
ultracentrifuge rotor made with UV light (b)
Densitometric trace of UV scan
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PREDICTED DENSITIES OF NEWLY REPLICATED
DNA MOLECULES ACCORDING TO THE THREE
HYPOTHESES ABOUT DNA REPLICATION
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14N15N
RESULTS OF CsCl GRADIENT ULTRACENTRIFUGATION EXPER
IMENT SHOWING DISTRIBUTION OF DNA DENSITY IN E.
coli CELLS AFTER 0 TO 4.1 GENERATIONS OF
GROWTH THIS EXPERIMENT ESTABLISHED THAT DNA
REPLICATION IS SEMICONSERVATIVE
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ELIMINATION OF DISPERSIVE REPLICATION MODEL
THROUGH DEMONSTRATION THAT THERE ARE NO
SINGLE-STRANDED DNA MOLECULES WITH A MXTURE OF
HEAVY AND LIGHT ISOTOPES AFTER ONE ROUND
OF REPLICATION
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Conclusion
1. DNA replication is semi-conservative 2. DNA
replication is dispersive
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DNA Replication Process
DNA
DNA
DNA
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THREE POSSIBLE WAYS IN WHICH DNA MIGHT BE
SYNTHESIZED AT THE REPLICATION FORK
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Control
Ligase is mutated
EXPERIMENTAL DEMONSTRATION OF SEMIDISCONTINUOUS
DNA REPLICATION (a) Replicating T4 DNA
pulse-labeled with radioactive precursor for
2-120 seconds (b) When T4 DNA ligase was mutated,
only small fragments of DNA were labeled