Plate 29 Bacterial Transduction. Genetic Changes 3 ways to alter the DNA within bacteria: Bacterial...
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Transcript of Plate 29 Bacterial Transduction. Genetic Changes 3 ways to alter the DNA within bacteria: Bacterial...
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
• 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
Generalized Transduction – Step 1
• Bacteriophages attach to specific receptors on the surface their host cell (they are species specific)
Generalized Transduction – Step 2
• Phage injects its DNA into the host bacteria cell
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
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
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
Specialized Transduction
• Some phages incorporate their DNA in the host cell’s DNA and don’t immediately assemble new phages
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
Specialized Transduction Animation
http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_3.html
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
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