MCB 3020C Final Exam V3 | MCB 3020C General Microbiology | Actual
Q&A with Rationale (MCB3020C Final Exam) | University of Central
Florida
1. Which of the following cellular structures is unique to Gram-positive bacteria and aids in
providing cell wall rigidity and antigenic specificity?
A. Teichoic acids
B. Lipopolysaccharide
C. Outer membrane
D. Periplasmic space
Answer: A
Explanation: Teichoic acids are polyalcohols linked to the peptidoglycan or plasma
membrane in Gram-positive bacteria, providing structural support and acting as surface
antigens. Unlike Gram-negative bacteria, which possess a complex outer membrane
containing lipopolysaccharides (LPS), Gram-positive cells have a much thicker layer of
peptidoglycan. This distinction is fundamental to the differential Gram stain technique used
to categorize bacterial species in clinical microbiology.
2. During the process of aerobic respiration in prokaryotes, what is the specific role of
molecular oxygen (O2)?
A. To serve as a source of electrons for the Electron Transport Chain
B. To function as a coenzyme in the Krebs cycle
C. To catalyze the conversion of glucose to pyruvate in glycolysis
D. To act as the final electron acceptor at the end of the Electron Transport Chain
Answer: D
Explanation: In aerobic respiration, oxygen functions as the terminal electron acceptor,
where it is reduced to water after receiving low-energy electrons from the transport chain.
This process allows for the regeneration of NAD+ and FAD, facilitating the continued flow
of the metabolic cycle. Without oxygen, the electron transport chain would stall,
significantly reducing the ATP yield per glucose molecule.
3. A bacterium that grows optimally at a temperature of 15°C and is found in Arctic waters
would be classified as a:
A. Mesophile
B. Psychrophile
,C. Hyperthermophile
D. Thermophile
Answer: B
Explanation: Psychrophiles are extremophilic organisms capable of growth and
reproduction in cold temperatures, typically ranging from -20 °C to +20 °C. Their enzymes
and membranes are specifically adapted to maintain fluidity and activity in freezing
environments. In contrast, mesophiles prefer moderate temperatures typical of human
pathogens, while thermophiles thrive in heat.
4. Which enzyme is primarily responsible for unwinding the DNA double helix at the
replication fork during bacterial DNA replication?
A. DNA Polymerase I
B. RNA Primase
C. DNA Ligase
D. DNA Helicase
Answer: D
Explanation: DNA Helicase utilizes ATP to break the hydrogen bonds between
complementary nitrogenous bases, effectively ‘unzipping’ the DNA strands. This action
creates the replication fork where DNA polymerase can begin synthesizing new daughter
strands. Following helicase, single-strand binding proteins stabilize the separated strands
to prevent them from re-annealing.
5. Which of the following best describes the function of the sigma factor in bacterial
transcription?
A. It recognizes the specific promoter sequence to initiate transcription
B. It catalyzes the elongation of the RNA transcript
C. It terminates transcription at the Rho-independent site
D. It adds a poly-A tail to the 3’ end of the mRNA
Answer: A
Explanation: The sigma factor is a subunit of bacterial RNA polymerase that ensures the
enzyme binds to the DNA at the correct promoter region. Once transcription begins and the
enzyme moves past the promoter, the sigma factor is typically released from the core
enzyme. This mechanism allows the cell to regulate gene expression by using different
sigma factors for various environmental conditions.
6. The ‘Endosymbiotic Theory’ proposes that mitochondria and chloroplasts evolved from:
A. Free-living prokaryotic cells
, B. Invaginations of the plasma membrane
C. Large viral particles
D. Spontaneous assembly of organic molecules
Answer: A
Explanation: Lynn Margulis championed this theory, which suggests that eukaryotic
organelles like mitochondria originated when a large anaerobic cell engulfed an aerobic
bacterium. Evidence supporting this includes the fact that these organelles possess their
own circular DNA, 70S ribosomes, and binary fission-like division. This symbiotic
relationship eventually became permanent, leading to the complex eukaryotic life we see
today.
7. In a bacterial growth curve, which phase is characterized by a period of little to no cell
division while the cells adjust to a new environment?
A. Death phase
B. Log phase
C. Stationary phase
D. Lag phase
Answer: D
Explanation: The lag phase is a preparatory stage where bacteria are metabolically active,
synthesizing enzymes and repairing any damage, but not yet dividing. The duration of this
phase depends on the health of the inoculum and the difference between the old and new
media. Once the adjustment is complete, the population enters the exponential or log phase
of rapid growth.
8. Which of the following is an example of horizontal gene transfer involving a bacterial virus
(bacteriophage)?
A. Transduction
B. Transformation
C. Conjugation
D. Binary fission
Answer: A
Explanation: Transduction occurs when a bacteriophage accidentally packages host
bacterial DNA into its capsid and delivers it to a new recipient cell. This differs from
conjugation, which requires cell-to-cell contact, and transformation, which involves the
uptake of naked DNA from the environment. Transduction can be either generalized (any
host DNA) or specialized (specific genes near the prophage insertion site).
Q&A with Rationale (MCB3020C Final Exam) | University of Central
Florida
1. Which of the following cellular structures is unique to Gram-positive bacteria and aids in
providing cell wall rigidity and antigenic specificity?
A. Teichoic acids
B. Lipopolysaccharide
C. Outer membrane
D. Periplasmic space
Answer: A
Explanation: Teichoic acids are polyalcohols linked to the peptidoglycan or plasma
membrane in Gram-positive bacteria, providing structural support and acting as surface
antigens. Unlike Gram-negative bacteria, which possess a complex outer membrane
containing lipopolysaccharides (LPS), Gram-positive cells have a much thicker layer of
peptidoglycan. This distinction is fundamental to the differential Gram stain technique used
to categorize bacterial species in clinical microbiology.
2. During the process of aerobic respiration in prokaryotes, what is the specific role of
molecular oxygen (O2)?
A. To serve as a source of electrons for the Electron Transport Chain
B. To function as a coenzyme in the Krebs cycle
C. To catalyze the conversion of glucose to pyruvate in glycolysis
D. To act as the final electron acceptor at the end of the Electron Transport Chain
Answer: D
Explanation: In aerobic respiration, oxygen functions as the terminal electron acceptor,
where it is reduced to water after receiving low-energy electrons from the transport chain.
This process allows for the regeneration of NAD+ and FAD, facilitating the continued flow
of the metabolic cycle. Without oxygen, the electron transport chain would stall,
significantly reducing the ATP yield per glucose molecule.
3. A bacterium that grows optimally at a temperature of 15°C and is found in Arctic waters
would be classified as a:
A. Mesophile
B. Psychrophile
,C. Hyperthermophile
D. Thermophile
Answer: B
Explanation: Psychrophiles are extremophilic organisms capable of growth and
reproduction in cold temperatures, typically ranging from -20 °C to +20 °C. Their enzymes
and membranes are specifically adapted to maintain fluidity and activity in freezing
environments. In contrast, mesophiles prefer moderate temperatures typical of human
pathogens, while thermophiles thrive in heat.
4. Which enzyme is primarily responsible for unwinding the DNA double helix at the
replication fork during bacterial DNA replication?
A. DNA Polymerase I
B. RNA Primase
C. DNA Ligase
D. DNA Helicase
Answer: D
Explanation: DNA Helicase utilizes ATP to break the hydrogen bonds between
complementary nitrogenous bases, effectively ‘unzipping’ the DNA strands. This action
creates the replication fork where DNA polymerase can begin synthesizing new daughter
strands. Following helicase, single-strand binding proteins stabilize the separated strands
to prevent them from re-annealing.
5. Which of the following best describes the function of the sigma factor in bacterial
transcription?
A. It recognizes the specific promoter sequence to initiate transcription
B. It catalyzes the elongation of the RNA transcript
C. It terminates transcription at the Rho-independent site
D. It adds a poly-A tail to the 3’ end of the mRNA
Answer: A
Explanation: The sigma factor is a subunit of bacterial RNA polymerase that ensures the
enzyme binds to the DNA at the correct promoter region. Once transcription begins and the
enzyme moves past the promoter, the sigma factor is typically released from the core
enzyme. This mechanism allows the cell to regulate gene expression by using different
sigma factors for various environmental conditions.
6. The ‘Endosymbiotic Theory’ proposes that mitochondria and chloroplasts evolved from:
A. Free-living prokaryotic cells
, B. Invaginations of the plasma membrane
C. Large viral particles
D. Spontaneous assembly of organic molecules
Answer: A
Explanation: Lynn Margulis championed this theory, which suggests that eukaryotic
organelles like mitochondria originated when a large anaerobic cell engulfed an aerobic
bacterium. Evidence supporting this includes the fact that these organelles possess their
own circular DNA, 70S ribosomes, and binary fission-like division. This symbiotic
relationship eventually became permanent, leading to the complex eukaryotic life we see
today.
7. In a bacterial growth curve, which phase is characterized by a period of little to no cell
division while the cells adjust to a new environment?
A. Death phase
B. Log phase
C. Stationary phase
D. Lag phase
Answer: D
Explanation: The lag phase is a preparatory stage where bacteria are metabolically active,
synthesizing enzymes and repairing any damage, but not yet dividing. The duration of this
phase depends on the health of the inoculum and the difference between the old and new
media. Once the adjustment is complete, the population enters the exponential or log phase
of rapid growth.
8. Which of the following is an example of horizontal gene transfer involving a bacterial virus
(bacteriophage)?
A. Transduction
B. Transformation
C. Conjugation
D. Binary fission
Answer: A
Explanation: Transduction occurs when a bacteriophage accidentally packages host
bacterial DNA into its capsid and delivers it to a new recipient cell. This differs from
conjugation, which requires cell-to-cell contact, and transformation, which involves the
uptake of naked DNA from the environment. Transduction can be either generalized (any
host DNA) or specialized (specific genes near the prophage insertion site).
