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Chapter 8 Outline

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

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Chapter 8 Outline

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  1. 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

  2. 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

  3. The Bacterial Genome • 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

  4. The Bacterial Genome • Extra chromosome, small circular DNA • Episomes – plasmids / F (fertility) factor

  5. 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

  6. Gene Transfer in Bacteria • Conjugation: • Direct transfer via connection tube, one-way traffic from donor cells to recipient cells. • It is not a reciprocal exchange of genetic information.

  7. Gene Transfer in Bacteria • Conjugation: • F+ cells donor cells containing F factor • F− cells recipient cells lacking F factor • Sex Pilus – connection tube

  8. Gene Transfer in Bacteria • 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

  9. Gene Transfer in Bacteria • 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.

  10. Gene Transfer in Bacteria • Conjugation: • Natural Gene Transfer and Antibiotic Resistance • Antibiotic resistance comes from the actions of genes located on R plasmids that can be transferred naturally.

  11. Gene Transfer in Bacteria • 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.

  12. Gene Transfer in Bacteria • Transformation: • A bacterium takes up DNA from the medium. • Recombination takes place between introduced genes and the bacterial chromosome.

  13. Gene Transfer in Bacteria • Transformation: • Competent cells: cells that take up DNA • Transformants: cells that receive genetic material • Cotransformed: cells that are transformed by two or more genes

  14. 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

  15. Gene Transfer in Bacteria • Transduction: • Bacterial viruses (bacteriophage) carry DNA from one bacterium to another. • Transduction usually occurs between bacteria of the same or closely related species.

  16. 8.2 Viruses Are Simple Replicating Systems Amenable To Genetic Analysis • 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.

  17. Techniques for the study of bacteriophages • Transduction: using phage to map bacterial genes • Generaltransduction: any genes can be transferred • Specializedtransduction: only a few genes can be transferred

  18. Techniques for the study of bacteriophages • Gene Mapping in Phages

  19. RNA Virus • Retrovirus: RNA viruses that have been integrated into the host genome • Reverse Transcriptase: synthesizing DNA from RNA or DNA template • HIV and AIDS

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