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Plate 29

Plate 29. Bacterial Transduction. Genetic Changes. 3 ways to alter the DNA within bacteria: Bacterial transformation Indirect: cell  extracellular fluid  cell Bacterial conjugation Direct: cell  cell Bacterial transduction Indirect: cell  virus  cell. Bacteriophage.

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Plate 29

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  1. Plate 29 Bacterial Transduction

  2. Genetic Changes • 3 ways to alter the DNA within bacteria: • Bacterial transformation • Indirect: cell  extracellular fluid  cell • Bacterial conjugation • Direct: cell  cell • Bacterial transduction • Indirect: cell  virus  cell

  3. Bacteriophage • Bacteriophage: a virus that specifically infects bacteria • Phage – Greek for “to eat” • Perhaps the most numerous “living thing” in the world • Composed of a protein capsid surrounding its DNA • Sometimes used as an alternative to antibiotics

  4. Generalized Transduction – Step 1 • Bacteriophages attach to specific receptors on the surface their host cell (they are species specific)

  5. Generalized Transduction – Step 2 • Phage injects its DNA into the host bacteria cell

  6. Generalized Transduction – Step 3 • Phage DNA instructs bacteria to create “fragmentation enzymes” to break up the host cell’s DNA • The bacteria cell begins building new phages, according to the phage DNA’s instructions • Some bacterial DNA segments are accidentally incorporated into the new phage’s DNA

  7. Generalized Transduction – Step 4 • Virus cycle culminates with lysis (rupturing) of the host cell • Hundreds of new bacteriophages are released, ready to infect other bacteria cells

  8. Generalized Transduction – Step 5 • New phages infect other bacteria cells and inject their DNA into the new host cell • If phage contained bacterial DNA from previous host, it may be incorporated into the new host cell’s DNA (like in conjugation) • New phages do not form

  9. Specialized Transduction • Some phages incorporate their DNA in the host cell’s DNA and don’t immediately assemble new phages

  10. Specialized Transduction • A chemical or a change in the host cell’s conditions signal the assembly of new phages • When the phage DNA detaches from the host cell DNA, it occasionally brings some bacterial DNA with it

  11. Specialized Transduction Animation http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_3.html

  12. Specialized Transduction • The new phages (with some bacterial DNA) leave the host cell when it lyses (ruptures) • Other bacterial cells can now be infected with the new hybrid DNA

  13. Generalized vs. Specialized Transduction • Generalized transduction is generalized because any of the host cell’s DNA can be incorporated into a new phage (it’s random) • Specialized transduction is specialized because only the host cell DNA that is next to the phage DNA can form in new phages

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