True of False (total of 6 points) Each answer must be justified

True of False (total of 6 points)
Each answer must be justified with a short explanation. 1 point per answer.
The phenotype of a bacteria can change without changing its genotype.
In bacteria, only one replisome is present.
All 3 horizontal gene transfer mechanisms discussed in class are common for both Gram-positive and Gram-negative cells.
The binding specificity of σ subunit of RNA polymerase is dependent on DNA sequence.
DNA regulatory elements such as enhancers are important transcriptional regulators in bacteria.
In prokaryotes, cell respiration occurs only when oxygen is present, anerobic bacteria obtain energy from fermentation.
Short answer questions (Total of 22 points)
Your supervisor gives you an E.coli stain (strain PIP) with an F plasmid on which is coded resistance for ampicillin. Your E.coli strain (strain ZAZ) is F- for the plasmid, and you would really like your strain to have ampicillin resistance. To favour conjugation, you grow both strains together for 2h (in broth) and plate agar containing ampicillin to grow single colonies overnight.
Figure 1. Schematic representation of the experimental plan.
In the morning, you find multiple colonies growing on your ampicillin resistant agar plates. Because you had mixed both strains in the same culture, you needed to be able to distinguish between which colony is a ZAZ or a PIP colony growing on your plate. Fortunately, your ZAZ strain grows blue on the plates, so they are easily identifiable.
To make sure the conjugation was successful, you choose 3 blue colonies and grow them in broth for 4h, then you isolate the plasmid and digest it with an enzyme that linearizes the plasmid. You know the F plasmid is 5,000bp long, which you use as a control (C) along your chosen 3 colonies. You run the plasmid on a gel and obtain the following result:
Figure 2. DNA gel of linearized plasmids isolated from experimental bacterial colonies. Marker is a standard measure of DNA fragment size. C= control plasmid. Experimental colonies are numbered 1 to 3.
The control F plasmid comes out at the expected size of 5kb, but all the colonies have plasmid that are bigger and not all the same size.
What do you think happened? How do you explain this result? (3points)
How can 2 different strains of the same bacteria (S. aureus for example) cause 2 different diseases? (4 points)
How can a virus cause cancer? What if it is an RNA virus, could it cause cancer too? How would that happen? (2 points)
 Around 2.5 billion years ago, something dramatic happened on earth, which has changed and influenced biology ever since. What was it and how did it happen? (2 points)
Discuss reasons why it is important to include diverse populations in studies of the human microbiome. (3 points)
What are the differences in electron acceptor and electron donors used by Escherichia coli (during aerobic cell respiration) and Acidithiobacillus thioparus (a sulfur chemolithotroph with the capacity for aerobic cell respiration)? (2 points)
What gives bacterial cell walls their structural integrity and why is that important. (2 points)
Explain the following observation: cells of E. coli fermenting glucose (anaerobic conditions) grow faster when NO3- is supplied to the culture, and then grow even faster when the culture is highly aerated. (2 points)
Shiga toxin (Stx) is a potent A-B toxin that inhibits protein synthesis and has a lethal dose 50 (LD50) of approximately 20 ng/kg of body weight in rabbits (meaning that 1 µg of Stx would be lethal for half the people exposed to this dose). Nonetheless, cell lines derived from different mammalian tissues range from highly susceptible (cytotoxic dose 50 [CD50] of approximately 10 pg/ml) to completely resistant (CD50 > 1 µg/ml). What cellular or molecular differences do you think account for susceptibility and resistance of these cell lines? (2 points)
LD50 is the dose at which 50% of the test subjects die. In this case, it was determined for rabbits given intravenous injections of the toxin.
CD50 is the concentration at which 50% of the cells die. Measure mostly used for tissue culture lab experiment.