chapter 8 outline
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Chapter 8 Outline. 8.1 Genetic Analysis of Bacteria Requires Special Approaches and Methods, 201 8.2 Viruses Are Simple Replicating Systems Amenable to Genetic Analysis, 218. 8.1 Genetic Analysis of Bacteria Requires Special Approaches and Methods. Techniques for the Study of Bacteria - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 8 Outline
• 8.1 Genetic Analysis of Bacteria Requires Special Approaches and Methods, 201
• 8.2 Viruses Are Simple Replicating Systems Amenable to Genetic Analysis, 218
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8.1 Genetic Analysis of Bacteria Requires Special Approaches and Methods
• Techniques for the Study of Bacteria
• Prototrophic – wild type• Auxotrophic – mutant type• Minimum medium: only required by
prototrophic bacteria• Complete medium: contain all substance
required by all bacteria, including auxotrophic bacteria
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• Mostly single, circular DNA molecule/chromosome• Single copy of most genes
• No dominant or recessive• Expressed or not
Little to no space between genes
No nucleus, so no separation of transcription and translation
The Bacterial Genome
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• Extra chromosome, small circular DNA
• Episomes – plasmids / F (fertility) factor
The Bacterial Genome
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Horizontal Transfer
•Movement of DNA from one bacterial cell to another•Results in change of individual cell within its life•Different from Vertical Transmission (inheritance)•3 main mechanisms
•Conjugation•Transformation•Transduction
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• Conjugation:
• Direct transfer via connection tube, one-way traffic from donor cells to recipient cells.
• It is not a reciprocal exchange of genetic information.
Gene Transfer in Bacteria
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• Conjugation:
• F+ cells donor cells containing F factor
• F− cells recipient cells lacking F factor
• Sex Pilus – connection tube
Gene Transfer in Bacteria
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• Conjugation:
• Hfr cells: (high-frequency strains) – donor cells with F factor integrated into the donor bacterial chromosome
• F prime (F′) cells: contain F plasmid carrying some bacterial genes
• Merozygotes: partial diploid bacterial cells containing F plasmid carrying some bacterial genes
Gene Transfer in Bacteria
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• Conjugation:
• Mapping bacterial genes with interrupted Conjugation: Distances between genes are measured by the time required for DNA transfer from Hfr cells to F− cells.
Gene Transfer in Bacteria
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• Conjugation:
• Natural Gene Transfer and Antibiotic Resistance
• Antibiotic resistance comes from the actions of genes located on R plasmids that can be transferred naturally.
Gene Transfer in Bacteria
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• Conjugation:
• Natural Gene Transfer and Antibiotic Resistance• Antibiotic resistance comes from the actions of
genes located on R plasmids that can be transferred naturally.• R plasmids have evolved in the past 60 years
since the beginning of widespread use of antibiotics.• The transfer of R plasmids is not restricted to
bacteria of the same or even related species.
Gene Transfer in Bacteria
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• Transformation:
• A bacterium takes up DNA from the medium.
• Recombination takes place between introduced genes and the bacterial chromosome.
Gene Transfer in Bacteria
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• Transformation:
• Competent cells: cells that take up DNA
• Transformants: cells that receive genetic material
• Cotransformed: cells that are transformed by two or more genes
Gene Transfer in Bacteria
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• Bacterial Genome Sequences:• 1 ~ 4 million base pairs of DNA
• Horizontal Gene Transfer:• Genes can be passed between individual
members of different species by nonreproductive mechanisms.
• Model Genetic Organism:• The bacterium Esherichia coli
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• Transduction:
• Bacterial viruses (bacteriophage) carry DNA from one bacterium to another.
• Transduction usually occurs between bacteria of the same or closely related species.
Gene Transfer in Bacteria
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• Virus: Replicating structure (DNA/RNA) + protein coat
• Bacteriophage: bacterial infection viruses
• Virulent phages: reproduce through the lytic cycle, and always kill the host cells.
• Temperate phages: inactive prophage–phage DNA integrates into bacterial chromosomes.
8.2 Viruses Are Simple Replicating Systems Amenable To Genetic Analysis
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• Transduction: using phage to map bacterial genes
• General transduction: any genes can be transferred
• Specialized transduction: only a few genes can be transferred
Techniques for the study of bacteriophages
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• Gene Mapping in Phages
Techniques for the study of bacteriophages
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• Retrovirus: RNA viruses that have been integrated into the host genome
• Reverse Transcriptase: synthesizing DNA from RNA or DNA template
• HIV and AIDS
RNA Virus
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