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TBR CBT #2 question

Discussion in 'MCAT Study Question Q&A' started by TheMightyBoosh, Jul 28, 2011.

  1. TheMightyBoosh

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    I have a question about the E. coli passage in TBR CBT #2, but I need to post a significant chunk of the passage for the question to make sense.

    Anyone know if I'm allowed to do that on here? Just making sure I don't anger any test prep reps (Berkeley Review Teach) :)
     
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  3. BerkReviewTeach

    BerkReviewTeach Company Rep & Bad Singer
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    I don't see a problem, but I can ask someone higher on the foodchain if you'd like. Maybe post it long enough to get some responses and then take it down if you're worried.
     
  4. TheMightyBoosh

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    OK here it goes....

    The relationship between a variety of bacteria and the viruses that infect them can be quantified in an experiment called the one-step growth experiment, so named for the single large burst (Figure 1) of plaque-forming units (PFU) it promotes (not for the number of steps in the experiment itself). It requires a PFU assay (Steps A-C below) to determine the number of infected bacterial cells and the number of bacteriophages

    ...

    One-Step Growth Experiment

    Phase I
    To synchronize infection, a concentrated 1-mL suspension of 109 bacterial cells is mixed with 108 phages.

    Phase II
    Incubation for 3 minutes allows for the adsorption of phage to 108 bacterial cells.

    Phase III
    To prevent new cycles of infection when progeny phage are released from host bacterial cells that were initially infected, the concentrated 1-mL suspension is diluted a millionfold, leaving 9 x 102 uninfected bacterial cells per milliliter.

    Phase IV
    The suspension is incubated in a flask for 60 minutes at 37 ˚C, and 1-mL aliquots are removed at various times to determine the PFU/mL.


    Initially, during the latent period, the number of plaques is constant. As the infected bacterial cells begin to lyse during the burst period, the number of plaques increases. After all of the infected cells have lysed, the concentration of bacteriophage remains constant (Figure 1).



    [​IMG]

    In a variation of the one-step growth experiment, chloroform and lysozyme can be added to each sample before plating. Bacterial cells (including those infected by the bacteriophages) are lysed, while the phages themselves remain unaffected. Immediately after infection, however, the phages disappear. This is referred to as the eclipse period (Figure 1). They reappear only toward the end of the latent period.

    136. In Figure 1, the latent period is longer than the eclipse period, because:
    A.
    it takes longer to assemble phages in the latent period than it does in the eclipse period.
    B. the phage lysozyme is synthesized late in the infection cycle.
    C. viral DNA replication proceeds more rapidly in the eclipse period than in the latent period.
    D. the phages in the extracellular suspension need more time to adsorb to their bacterial hosts.

    I'm really confused as to what the eclipse period actually is and how it compares to the latent phase. In the variation of the experiment, is lysozyme added while the phages are in their latent period?
     
  5. TheMightyBoosh

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    #4 TheMightyBoosh, Jul 29, 2011
    Last edited: Jul 29, 2011
  6. TheMightyBoosh

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