BIOS 242 MICROBIOLOGY FINAL EXAM
STUDY GUIDE QUESTIONS WITH
VERIFIED ANSWERS
1. Which enzyme is responsible for relieving torsional strain ahead of the replication fork
during bacterial DNA replication?
A. DNA Gyrase (Topoisomerase II)
B. DNA Polymerase III
C. Helicase
D. Primase
Answer: A
Conceptual Explanation: DNA Gyrase, a type of topoisomerase, introduces negative
supercoils to relieve the tension caused by the unwinding of the DNA double helix by
helicase.
2. In the lac operon, what occurs when lactose is present but glucose is also present in high
concentrations?
A. High levels of cAMP lead to maximum transcription.
,B. The repressor remains bound to the operator.
C. The structural genes are not transcribed at all.
D. Transcription occurs at a low, basal level because CAP is inactive.
Answer: D
Conceptual Explanation: When glucose is present, cAMP levels are low, so the Catabolite
Activator Protein (CAP) does not bind to the promoter. Even if lactose removes the
repressor, transcription remains inefficient.
3. Which of the following is a characteristic of the Gram-negative cell wall that is absent in
Gram-positive bacteria?
A. Peptidoglycan
B. Lipopolysaccharide (LPS)
C. Teichoic acids
D. Cytoplasmic membrane
Answer: B
Conceptual Explanation: Gram-negative bacteria possess an outer membrane containing
Lipopolysaccharide (LPS), which acts as an endotoxin. Teichoic acids are found in Gram-
positive walls.
, 4. During the process of oxidative phosphorylation, what is the direct source of energy used
to power ATP synthase?
A. The proton motive force (H+ gradient)
B. The reduction of O2 to H2O
C. The oxidation of NADH to NAD+
D. The hydrolysis of GTP
Answer: A
Conceptual Explanation: ATP synthase uses the flow of protons down their
electrochemical gradient (proton motive force) across the inner mitochondrial or bacterial
membrane to catalyze ATP synthesis.
5. Which type of horizontal gene transfer requires a bacteriophage as a vector?
A. Conjugation
B. Transduction
C. Transformation
D. Transposition
Answer: B
Conceptual Explanation: Transduction is the process by which DNA is transferred from
one bacterium to another by a virus (bacteriophage).
STUDY GUIDE QUESTIONS WITH
VERIFIED ANSWERS
1. Which enzyme is responsible for relieving torsional strain ahead of the replication fork
during bacterial DNA replication?
A. DNA Gyrase (Topoisomerase II)
B. DNA Polymerase III
C. Helicase
D. Primase
Answer: A
Conceptual Explanation: DNA Gyrase, a type of topoisomerase, introduces negative
supercoils to relieve the tension caused by the unwinding of the DNA double helix by
helicase.
2. In the lac operon, what occurs when lactose is present but glucose is also present in high
concentrations?
A. High levels of cAMP lead to maximum transcription.
,B. The repressor remains bound to the operator.
C. The structural genes are not transcribed at all.
D. Transcription occurs at a low, basal level because CAP is inactive.
Answer: D
Conceptual Explanation: When glucose is present, cAMP levels are low, so the Catabolite
Activator Protein (CAP) does not bind to the promoter. Even if lactose removes the
repressor, transcription remains inefficient.
3. Which of the following is a characteristic of the Gram-negative cell wall that is absent in
Gram-positive bacteria?
A. Peptidoglycan
B. Lipopolysaccharide (LPS)
C. Teichoic acids
D. Cytoplasmic membrane
Answer: B
Conceptual Explanation: Gram-negative bacteria possess an outer membrane containing
Lipopolysaccharide (LPS), which acts as an endotoxin. Teichoic acids are found in Gram-
positive walls.
, 4. During the process of oxidative phosphorylation, what is the direct source of energy used
to power ATP synthase?
A. The proton motive force (H+ gradient)
B. The reduction of O2 to H2O
C. The oxidation of NADH to NAD+
D. The hydrolysis of GTP
Answer: A
Conceptual Explanation: ATP synthase uses the flow of protons down their
electrochemical gradient (proton motive force) across the inner mitochondrial or bacterial
membrane to catalyze ATP synthesis.
5. Which type of horizontal gene transfer requires a bacteriophage as a vector?
A. Conjugation
B. Transduction
C. Transformation
D. Transposition
Answer: B
Conceptual Explanation: Transduction is the process by which DNA is transferred from
one bacterium to another by a virus (bacteriophage).
