BIOL 3200 Exam 2 Actual Exam V1 | BIOL 3200 General Microbiology
(BIOL 3200 Exam 2) | Auburn University
1. Which of the following best describes the function of an apoenzyme?
A. The protein portion of an enzyme that is inactive without a cofactor.
B. The complete, active form of an enzyme including its cofactor.
C. A non-protein organic molecule that assists in enzyme catalysis.
D. An inorganic ion that stabilizes the enzyme-substrate complex.
Answer: A
Rationale: An apoenzyme is specifically the protein component of an enzyme that requires
a cofactor to become catalytically active. When the apoenzyme combines with its specific
cofactor, it forms a holoenzyme. This distinction is crucial in microbiology as many
metabolic pathways depend on the availability of these non-protein components to
function.
2. In the context of microbial metabolism, what is the net yield of ATP and NADH from one
molecule of glucose during the Emden-Meyerhof-Parnas (EMP) pathway?
A. 4 ATP and 2 NADH
B. 2 ATP and 2 NADH
C. 2 ATP and 4 NADH
D. 1 ATP and 1 NADH
Answer: B
Rationale: The EMP pathway, which is the most common form of glycolysis, involves a
preparatory phase that consumes 2 ATP and a payoff phase that produces 4 ATP.
Consequently, the net gain for the cell is 2 ATP per glucose molecule. Additionally, two
molecules of NAD+ are reduced to NADH during the oxidation of glyceraldehyde-3-
phosphate.
3. Which enzyme is responsible for unwinding the DNA double helix at the replication fork
during bacterial DNA replication?
A. DNA Polymerase III
B. Helicase
C. DNA Gyrase
D. Primase
,Answer: B
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the two
strands of the DNA molecule to create the replication fork. While DNA gyrase helps relieve
the tension caused by supercoiling ahead of the fork, it is helicase that physically separates
the strands. This process is energy-dependent, requiring ATP hydrolysis to move along the
DNA.
4. During aerobic respiration in bacteria, what is the final electron acceptor in the electron
transport chain?
A. Nitrate (NO3-)
B. Sulfate (SO4 2-)
C. Oxygen (O2)
D. Pyruvate
Answer: C
Rationale: Aerobic respiration is defined by the use of molecular oxygen as the terminal
electron acceptor at the end of the electron transport chain. Oxygen has a high reduction
potential, allowing for the maximum extraction of energy from the flow of electrons. In
contrast, anaerobic respiration uses inorganic molecules like nitrate or sulfate as acceptors.
5. Which of the following processes allows for the recycling of NAD+ so that glycolysis can
continue in the absence of an electron transport chain?
A. The TCA Cycle
B. Chemiosmosis
C. Fermentation
D. Photophosphorylation
Answer: C
Rationale: Fermentation is a metabolic strategy used by microbes to maintain redox
balance when respiration is not possible. It involves the reduction of an internal organic
metabolite, such as pyruvate, to regenerate NAD+ from NADH. This regeneration is vital
because the cell has a limited supply of NAD+, which is required for the oxidation steps of
glycolysis.
6. The ‘wobble hypothesis’ explains why:
A. DNA polymerase makes errors during replication.
B. Sigma factors can recognize different promoter regions.
C. Ribosomes can bind to any part of the mRNA sequence.
, D. The genetic code is redundant, and multiple codons can code for the same amino acid.
Answer: D
Rationale: The wobble hypothesis suggests that the base at the 5’ end of the tRNA
anticodon can form non-standard hydrogen bonds with the 3’ base of the mRNA codon.
This flexibility allows a single tRNA to recognize more than one codon. Consequently, this
mechanism explains the degeneracy of the genetic code where 61 codons specify only 20
amino acids.
7. In the lac operon of E. coli, what happens when lactose is present and glucose is absent?
A. The repressor binds to the operator, and transcription is blocked.
B. Allolactose binds to the repressor, and CAP-cAMP binds to the promoter, leading to high
transcription.
C. cAMP levels are low, and the CAP protein does not bind to the promoter.
D. The RNA polymerase is degraded to prevent wasteful enzyme synthesis.
Answer: B
Rationale: High transcription of the lac operon requires both the removal of the repressor
and the activation by CAP-cAMP. Lactose is converted to allolactose, which acts as an
inducer by binding the repressor and preventing it from blocking the operator.
Simultaneously, low glucose levels lead to high cAMP, which helps RNA polymerase bind
efficiently to the promoter.
8. Which of the following is a key difference between oxygenic and anoxygenic
photosynthesis?
A. Oxygenic photosynthesis does not involve a light-harvesting complex.
B. Anoxygenic photosynthesis occurs in the chloroplasts of bacteria.
C. Oxygenic photosynthesis uses H2O as an electron donor, while anoxygenic does not.
D. Anoxygenic photosynthesis produces ATP through substrate-level phosphorylation.
Answer: C
Rationale: Oxygenic photosynthesis, performed by cyanobacteria and plants, splits water
molecules to provide electrons, releasing oxygen as a byproduct. Anoxygenic
photosynthesis, performed by organisms like purple sulfur bacteria, uses other electron
donors such as H2S or H2. Because they do not split water, these bacteria do not produce
oxygen during the process.
9. Which repair mechanism uses the enzyme photolyase to fix thymine dimers caused by UV
light?
A. Light Repair (Photoreactivation)
(BIOL 3200 Exam 2) | Auburn University
1. Which of the following best describes the function of an apoenzyme?
A. The protein portion of an enzyme that is inactive without a cofactor.
B. The complete, active form of an enzyme including its cofactor.
C. A non-protein organic molecule that assists in enzyme catalysis.
D. An inorganic ion that stabilizes the enzyme-substrate complex.
Answer: A
Rationale: An apoenzyme is specifically the protein component of an enzyme that requires
a cofactor to become catalytically active. When the apoenzyme combines with its specific
cofactor, it forms a holoenzyme. This distinction is crucial in microbiology as many
metabolic pathways depend on the availability of these non-protein components to
function.
2. In the context of microbial metabolism, what is the net yield of ATP and NADH from one
molecule of glucose during the Emden-Meyerhof-Parnas (EMP) pathway?
A. 4 ATP and 2 NADH
B. 2 ATP and 2 NADH
C. 2 ATP and 4 NADH
D. 1 ATP and 1 NADH
Answer: B
Rationale: The EMP pathway, which is the most common form of glycolysis, involves a
preparatory phase that consumes 2 ATP and a payoff phase that produces 4 ATP.
Consequently, the net gain for the cell is 2 ATP per glucose molecule. Additionally, two
molecules of NAD+ are reduced to NADH during the oxidation of glyceraldehyde-3-
phosphate.
3. Which enzyme is responsible for unwinding the DNA double helix at the replication fork
during bacterial DNA replication?
A. DNA Polymerase III
B. Helicase
C. DNA Gyrase
D. Primase
,Answer: B
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the two
strands of the DNA molecule to create the replication fork. While DNA gyrase helps relieve
the tension caused by supercoiling ahead of the fork, it is helicase that physically separates
the strands. This process is energy-dependent, requiring ATP hydrolysis to move along the
DNA.
4. During aerobic respiration in bacteria, what is the final electron acceptor in the electron
transport chain?
A. Nitrate (NO3-)
B. Sulfate (SO4 2-)
C. Oxygen (O2)
D. Pyruvate
Answer: C
Rationale: Aerobic respiration is defined by the use of molecular oxygen as the terminal
electron acceptor at the end of the electron transport chain. Oxygen has a high reduction
potential, allowing for the maximum extraction of energy from the flow of electrons. In
contrast, anaerobic respiration uses inorganic molecules like nitrate or sulfate as acceptors.
5. Which of the following processes allows for the recycling of NAD+ so that glycolysis can
continue in the absence of an electron transport chain?
A. The TCA Cycle
B. Chemiosmosis
C. Fermentation
D. Photophosphorylation
Answer: C
Rationale: Fermentation is a metabolic strategy used by microbes to maintain redox
balance when respiration is not possible. It involves the reduction of an internal organic
metabolite, such as pyruvate, to regenerate NAD+ from NADH. This regeneration is vital
because the cell has a limited supply of NAD+, which is required for the oxidation steps of
glycolysis.
6. The ‘wobble hypothesis’ explains why:
A. DNA polymerase makes errors during replication.
B. Sigma factors can recognize different promoter regions.
C. Ribosomes can bind to any part of the mRNA sequence.
, D. The genetic code is redundant, and multiple codons can code for the same amino acid.
Answer: D
Rationale: The wobble hypothesis suggests that the base at the 5’ end of the tRNA
anticodon can form non-standard hydrogen bonds with the 3’ base of the mRNA codon.
This flexibility allows a single tRNA to recognize more than one codon. Consequently, this
mechanism explains the degeneracy of the genetic code where 61 codons specify only 20
amino acids.
7. In the lac operon of E. coli, what happens when lactose is present and glucose is absent?
A. The repressor binds to the operator, and transcription is blocked.
B. Allolactose binds to the repressor, and CAP-cAMP binds to the promoter, leading to high
transcription.
C. cAMP levels are low, and the CAP protein does not bind to the promoter.
D. The RNA polymerase is degraded to prevent wasteful enzyme synthesis.
Answer: B
Rationale: High transcription of the lac operon requires both the removal of the repressor
and the activation by CAP-cAMP. Lactose is converted to allolactose, which acts as an
inducer by binding the repressor and preventing it from blocking the operator.
Simultaneously, low glucose levels lead to high cAMP, which helps RNA polymerase bind
efficiently to the promoter.
8. Which of the following is a key difference between oxygenic and anoxygenic
photosynthesis?
A. Oxygenic photosynthesis does not involve a light-harvesting complex.
B. Anoxygenic photosynthesis occurs in the chloroplasts of bacteria.
C. Oxygenic photosynthesis uses H2O as an electron donor, while anoxygenic does not.
D. Anoxygenic photosynthesis produces ATP through substrate-level phosphorylation.
Answer: C
Rationale: Oxygenic photosynthesis, performed by cyanobacteria and plants, splits water
molecules to provide electrons, releasing oxygen as a byproduct. Anoxygenic
photosynthesis, performed by organisms like purple sulfur bacteria, uses other electron
donors such as H2S or H2. Because they do not split water, these bacteria do not produce
oxygen during the process.
9. Which repair mechanism uses the enzyme photolyase to fix thymine dimers caused by UV
light?
A. Light Repair (Photoreactivation)
