2025 SEA- PHAGES LAB FINAL EXAM WITH
ACTUAL QUESTIONS AND CORRECTLY
WELL DEFINED ANSWERS LATEST ALREADY
GRADED A+
If you have a bacterial contamination on a plate that you wish to flood, should
you? Why? - ANSWERS-Yes --> the bacteria is being filtered
will the phage continue to reproduce after the MTL is calculated? why? -
ANSWERS-no --> the bacterial host is no longer present so it cannot reproduce
*What do we mean when we refer to the burst size of a phage? How will burst
size affect your titer?* - ANSWERS-burst size - the number of phage particles
produced per infected bacterium.
Two large biological molecules that compose a phage are: - ANSWERS-proteins
and nucleotides
describe the lytic and lysogenic cycle - ANSWERS-bacteriophage infection results
in either a lytic or a lysogenic cycle:
, 1. LYTIC CYCLE results in the production of new progeny that cause the cell to lyse
2. LYSOGENIC CYCLE results in incorporation of the viral DNA into the bacterial
DNA where it remains inactive
-- a lysogenic cycle may progress into a lytic cycle
*a bacterium in which a phage has incorporated its genome is called a* -
ANSWERS-lysogen
Why do we add the top agar to section 3 of the three-phase streak plate? How
does this relate to the fact that we shouldn't swirl the streak plate? - ANSWERS-
Section 3 is where the most diluted phage exists. Top agar is added to section 3 so
it will flow through sections 1 and 2 without crossing the different sections. We
shouldn't swirl the streak plate because this would cause the sections to cross and
potential lysis of the entire plate.
Suppose you are lucky and isolate a phage from your soil sample that produces
clear 2.0 mm plaques on a M. smeg lawn. You want to do another streak plate but
there is no more M. smeg so you grab a culture tube of E. coli instead. Would you
expect to see the same results after 48 hours? Why? - ANSWERS-No -- only
certain phages will grow with certain host bacteria
When we filter-sterilize our sample with the 0.22 mm filters, why do we still
expect to find phages in the sample? - ANSWERS-the phages are small enough to
be filtered through
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