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MCB 301 Final Exam with questions & 100% Correct & Verified Answers
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MCB 301 Final Exam with questions & 100% Correct & Verified Answers
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MCB 301 Final Exam with questions & 100%Correct & Verified Answers
An MCB301 student is developing a dichotomous key with the following bacteria:
Staphylococcus aureus, Citrobacter freundii, Bacillus subtilis, Proteus vulgaris and
Enterococcus faecium. The student wanted to start the key with the indole production
characteristic. In this case, why would this characteristic not normally be used first? -
✔✔Usually a dichotomous key begins with a characteristic that separates the group
of organisms in half. In the above case, it would only separate out one organism from
the other four. (2 pts)
As discussed in lecture, water from a water treatment plant is usually analyzed for what
type of microorganism, and why? - ✔✔The presence and identification of enterics (or
coliforms, or Escherichia coli) is usually performed on water. (1 pt)
The presence of enterics in water indicates that the water is contaminated with stool or
feces (which is composed of enterics). Stool could also contain certain pathogens
(especially those that cause diarrhea) and thus the contaminated water would be unsafe
to drink. (1 pt)
Why would a mutation in a bacterial genome more likely cause a misidentification of a
bacterium when using a dichotomous key than a "best fit" method? - ✔✔A mutation
could change the result of a single biochemical test so that it results in going down the
wrong pathway of the key and misidentification of the bacterium will occur. (1 pt)
However, with the "best fit" method, several biochemical tests are done at once to find
a bacterium that most likely possesses those characteristics (a perfect match may not
have to occur to find a likely candidate). (1 pt)
The 16S rRNA gene is ideal for PCR amplification and determination of bacterial species.
Explain how it is ideal. - ✔✔The 16S rRNA gene is found in all bacteria and contains
,conserved sequences so that it can be amplified from all of those bacterial species
(using "universal" PCR primers). (1 pt) Note: it is also only about 1,500 bp long and can
be amplified easily.
The 16S rRNA gene also contains variable sequences unique to each bacterial species. So
sequencing of the gene and searching databases of 16S rRNA gene sequences from
known bacteria, can help determine the identity of the microorganism. (1 pt)
Why would a mutation in a bacterial genome more likely cause a misidentification of a
bacterium when using a dichotomous key than a "best fit" method? - ✔✔A mutation
could change the result of a single biochemical test so that it results in going down the
wrong pathway of the key and misidentification of the bacterium will occur. (1 pt)
However, with the "best fit" method, several biochemical tests are done at once to find
a bacterium that most likely possesses those characteristics (a perfect match may not
have to occur to find a likely candidate). (1 pt)
As discussed in the Identification lecture, what is a plaque and how can the formation of
a plaque be used in the identification of a bacterium? Note: in this question, the term
"plaque" does not refer to growth of a biofilm on a tooth surface. - ✔✔A plaque is a
clear zone formed in a lawn of bacterial growth where cells have lysed because they
became infected by a virus. (1 pt)
This would indicate that the bacterium is susceptible to infection by that particular virus
(the bacterial cell must possess the appropriate receptor recognized by the phage to
infect that cell). Each bacterial species is susceptible to specific phage, so an unknown
bacterium may be identified if it can be shown to be susceptibility to the same set of
specific phage as a known bacterium. (1 pt)
Describe how an Enterotube (Enteropluri Tube) is inoculated and used to help identify a
bacterial organism. - ✔✔The tube contains several individual compartments, each
, with a different selective/differential medium. A wire runs through the middle of each
compartment so all of the media can be inoculated quickly. This is performed by
touching one end of the wire to a bacterial colony and pulling and then pushing the wire
through the tube. (1 pt)
The tube is incubated to allow growth, and then the tests are scored (usually by looking
for color changes; some compartments require reagents to be added). The test results
are compared to a database of results from known bacteria to identify the
microorganism. (1 pt)
In the Transposon Mutagenesis Exercise, what four genes important for the conjugation
process are located on the chromosome of the donor strain? - ✔✔Genes that encode
the sex pilus, mating bridge, nicking enzyme, and DNA polymerase.
In the Transposon Mutagenesis Exercise, why can't the donor cells grow on the medium
serving as a negative control? Explain your answer. - ✔✔The medium used as a
negative control (i.e., LB Kan) does not contain DAP. (1 pt)
Since the donor cell cannot synthesize its own DAP it needs it preformed in the medium.
Otherwise, when the bacterium grows it cannot form a strong cell wall and it will be
killed by osmotic lysis. (1 pt)
The recipient cell used in the transposon mutagenesis experiment can do aerobic
respiration. Based on further information about the recipient cell that you were given, is
the recipient an obligate aerobe, obligate anaerobe, facultative aerobe, microaerophile,
or aerotolerant anaerobe, and why? - ✔✔The recipient bacterium is a facultative
aerobe (1 pt) because it can also perform fermentation (1 pt)
If pRL27 does not have an oriT site, then our Transposon Mutagenesis Experiment would
be unsuccessful in generating the proper mutants. How would the lack of an oriT site
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