Biol 320 Exam 2
BIOL 320 EXAM 2 NEWEST 2025 ACTUAL EXAM COMPLETE
QUESTIONS AND CORRECT ANSWERS(VERIFIED ANSWERS)
|ALREADY GRADED A+
Expression of this operon is controlled by a transcriptional regulator. The transcriptional
regulator is controlled by the presence of xylose; it is bound to the DNA in the absence of
xylose, when transcription of the xyl operon is low/decreased. Which of the following would
best describe this situation?
a.) This regulator is a repressor, and xylose acts as a co-repressor.
b.) The regulator is a repressor, and xylose acts as an inducer.
c.) The regulator is an activator, and xylose acts as an inducer.
d.) The regulator is an activator, and xylose acts as an inhibitor. - ANSWER-b.) The regulator is a
repressor, and xylose acts as an inducer.
T or F: Denitrification results in loss of bioavailable nitrogen and production to gaseous
products, and its typically performed by facultative anaerobes (that could instead use O2, if it
were present). - ANSWER-True
T or F: Oxygenic photosynthesis uses water as an electron donor, while anoxygenic
photosynthesis uses other molecules (e.g. H2S) as electron donors; however, both of these
processes produce ATP by oxidative photosynthesis via electron transportation and production
of a proton motive force. - ANSWER-True
T or F: Selection is usually not necessary when looking for cells that have taken up DNA by
transformation or conjugation, because the frequency of these processes is high (nearly all cells
take up DNA). - ANSWER-False
1|Page
, Biol 320 Exam 2
T or F: NAD+/NADH is an important electron carrier for cells that carry out respiration, however
this electron carrier is not used in cells that only carry out fermentation. - ANSWER-False
Phase variation involves uptake of genes by conjugation, which causes a switch between aerobic
respiration and anaerobic respiration. - ANSWER-False
T or F: If a plasmid is to be replicated inside a cell, it must have some type of origin of replication
(oriC). - ANSWER-True
T or F: Assimilatory reduction of nitrogen or sulfur is typically not coupled to electron transport
or energy production, and is mainly used uptake of compounds for use as nitrogen or sulfur
sources. - ANSWER-True
T or F: The TCA cycle and glycolysis are only important for catabolism of glucose in E. coli,
whereas breakdown of other substrates require completely different pathways/cyclers. -
ANSWER-False
Which of the following would most accurately describe the purpose of sigma factors in
bacteria?
a.) They are the catalytic subunit of the RNA polymerase.
b.) They bind to operators and prevent binding of RNA polymerase, thus regulating
transcription.
c.) They allow RNA polymerase to bind to and initiate transcription from specific sets of
promoters.
d.) They are produced by certain types of Bacteria as a way of sensing cell density.
e.) They allow transcripts to bind the ribosome and initiate translation. - ANSWER-c.) They allow
RNA polymerase to bind to and initiate transcription from specific sets of promoters.
2|Page
, Biol 320 Exam 2
What type of mutation would a transposon cause (after transposition to a new DNA fragment)?
a.) A large deletion mutation
b.) A point mutation
c.) A transition mutation
d.) A large insertion mutation - ANSWER-d.) A large insertion mutation
Of the following redox couples, circle the one that would represent the best electron donor
(molecule on the right side of the slash)?
a.) Sº/HS
b.) SO4^2-/HSO3-
c.) Fe^3+/Fe^2+
d.) H+/H2
e.) NO3-/NO2- - ANSWER-b.) SO4^2-/HSO3-
Of the following redox couples, circle the one that would represent the best electron acceptor
(molecule on the left side of the slash)?
a.) Sº/HS
b.) SO4^2-/HSO3-
c.) Fe^3+/Fe^2+
d.) H+/H2
e.) NO3-/NO2- - ANSWER-c.) Fe^3+/Fe^2+
3|Page
, Biol 320 Exam 2
You have isolated an anaerobic organism that is capable of using H2 as an electron donor and
either Sº (elemental) sulfur, reduced to HS-) or HSO3- (reduced to HS-). When grown in the
presence of H2, HSO3-, and Sº, would you expect (based solely on energetic terms) the
organism to preferentially use HSO3- or Sº, or would it have no preference? Why? - ANSWER-
answer!
Use HSO3- only because it is further down the electron tower, making it a better electron
acceptor.
Would an organism using H2 (being oxidized to H+) as an electron donor necessarily be required
to use reverse electron transport to make reduced NADH for biosynthesis? How about if the
organism was using NO2- (nitrite) as an electron donor (being oxidized to NO3-, nitrate)? Why
or why not? - ANSWER-answer!
H2, No because it is higher on the e- tower making it a better electron donor for --> NADH. NO2-
requires reverse electron because it is placed below NADH on the electron tower.
Draw a schematic of an operon or two protein coding genes involved in catabolism of the sugar
xylose (let's call them xylA and xylB) in a polycistronic message in a bacterium. Also, draw the
resulting RNA transcript, and regions of the transcript that would result in the proteins. Indicate
all necessary regions that would be required for transcription of the DNA and translation of the
RNA intothwo separate proteins XylA and XylB. - ANSWER-draw!
Which of the following is the typical size of a bacterial genome?
a.) 1-10 kbp (kilobase pairs)
b.) 10-100 kbp
c.) 1-10 Mbp (megabase pairs)
d.) 1-10 Gbp (gigabase pairs)
e.) 10-100 Gbp - ANSWER-c.) 1-10 Mbp (megabase pairs)
4|Page
BIOL 320 EXAM 2 NEWEST 2025 ACTUAL EXAM COMPLETE
QUESTIONS AND CORRECT ANSWERS(VERIFIED ANSWERS)
|ALREADY GRADED A+
Expression of this operon is controlled by a transcriptional regulator. The transcriptional
regulator is controlled by the presence of xylose; it is bound to the DNA in the absence of
xylose, when transcription of the xyl operon is low/decreased. Which of the following would
best describe this situation?
a.) This regulator is a repressor, and xylose acts as a co-repressor.
b.) The regulator is a repressor, and xylose acts as an inducer.
c.) The regulator is an activator, and xylose acts as an inducer.
d.) The regulator is an activator, and xylose acts as an inhibitor. - ANSWER-b.) The regulator is a
repressor, and xylose acts as an inducer.
T or F: Denitrification results in loss of bioavailable nitrogen and production to gaseous
products, and its typically performed by facultative anaerobes (that could instead use O2, if it
were present). - ANSWER-True
T or F: Oxygenic photosynthesis uses water as an electron donor, while anoxygenic
photosynthesis uses other molecules (e.g. H2S) as electron donors; however, both of these
processes produce ATP by oxidative photosynthesis via electron transportation and production
of a proton motive force. - ANSWER-True
T or F: Selection is usually not necessary when looking for cells that have taken up DNA by
transformation or conjugation, because the frequency of these processes is high (nearly all cells
take up DNA). - ANSWER-False
1|Page
, Biol 320 Exam 2
T or F: NAD+/NADH is an important electron carrier for cells that carry out respiration, however
this electron carrier is not used in cells that only carry out fermentation. - ANSWER-False
Phase variation involves uptake of genes by conjugation, which causes a switch between aerobic
respiration and anaerobic respiration. - ANSWER-False
T or F: If a plasmid is to be replicated inside a cell, it must have some type of origin of replication
(oriC). - ANSWER-True
T or F: Assimilatory reduction of nitrogen or sulfur is typically not coupled to electron transport
or energy production, and is mainly used uptake of compounds for use as nitrogen or sulfur
sources. - ANSWER-True
T or F: The TCA cycle and glycolysis are only important for catabolism of glucose in E. coli,
whereas breakdown of other substrates require completely different pathways/cyclers. -
ANSWER-False
Which of the following would most accurately describe the purpose of sigma factors in
bacteria?
a.) They are the catalytic subunit of the RNA polymerase.
b.) They bind to operators and prevent binding of RNA polymerase, thus regulating
transcription.
c.) They allow RNA polymerase to bind to and initiate transcription from specific sets of
promoters.
d.) They are produced by certain types of Bacteria as a way of sensing cell density.
e.) They allow transcripts to bind the ribosome and initiate translation. - ANSWER-c.) They allow
RNA polymerase to bind to and initiate transcription from specific sets of promoters.
2|Page
, Biol 320 Exam 2
What type of mutation would a transposon cause (after transposition to a new DNA fragment)?
a.) A large deletion mutation
b.) A point mutation
c.) A transition mutation
d.) A large insertion mutation - ANSWER-d.) A large insertion mutation
Of the following redox couples, circle the one that would represent the best electron donor
(molecule on the right side of the slash)?
a.) Sº/HS
b.) SO4^2-/HSO3-
c.) Fe^3+/Fe^2+
d.) H+/H2
e.) NO3-/NO2- - ANSWER-b.) SO4^2-/HSO3-
Of the following redox couples, circle the one that would represent the best electron acceptor
(molecule on the left side of the slash)?
a.) Sº/HS
b.) SO4^2-/HSO3-
c.) Fe^3+/Fe^2+
d.) H+/H2
e.) NO3-/NO2- - ANSWER-c.) Fe^3+/Fe^2+
3|Page
, Biol 320 Exam 2
You have isolated an anaerobic organism that is capable of using H2 as an electron donor and
either Sº (elemental) sulfur, reduced to HS-) or HSO3- (reduced to HS-). When grown in the
presence of H2, HSO3-, and Sº, would you expect (based solely on energetic terms) the
organism to preferentially use HSO3- or Sº, or would it have no preference? Why? - ANSWER-
answer!
Use HSO3- only because it is further down the electron tower, making it a better electron
acceptor.
Would an organism using H2 (being oxidized to H+) as an electron donor necessarily be required
to use reverse electron transport to make reduced NADH for biosynthesis? How about if the
organism was using NO2- (nitrite) as an electron donor (being oxidized to NO3-, nitrate)? Why
or why not? - ANSWER-answer!
H2, No because it is higher on the e- tower making it a better electron donor for --> NADH. NO2-
requires reverse electron because it is placed below NADH on the electron tower.
Draw a schematic of an operon or two protein coding genes involved in catabolism of the sugar
xylose (let's call them xylA and xylB) in a polycistronic message in a bacterium. Also, draw the
resulting RNA transcript, and regions of the transcript that would result in the proteins. Indicate
all necessary regions that would be required for transcription of the DNA and translation of the
RNA intothwo separate proteins XylA and XylB. - ANSWER-draw!
Which of the following is the typical size of a bacterial genome?
a.) 1-10 kbp (kilobase pairs)
b.) 10-100 kbp
c.) 1-10 Mbp (megabase pairs)
d.) 1-10 Gbp (gigabase pairs)
e.) 10-100 Gbp - ANSWER-c.) 1-10 Mbp (megabase pairs)
4|Page
