BIO 171 BASIC MICROBIOLOGY FINAL
PRACTICE EXAM 2026
1. Which of the following components is unique to the cell wall of Gram-positive bacteria and
functions in cation transport and antigenic specificity?
A. Lipopolysaccharide (LPS)
B. N-acetylmuramic acid
C. Outer membrane protein A (OmpA)
D. Teichoic acids
Answer: D
Conceptual Explanation: Teichoic acids are poly-alcohol phosphates found in Gram-
positive cell walls that help regulate cation movement and provide antigenic variation; LPS
is specific to Gram-negatives.
2. During the process of endospore formation, what is the specific role of dipicolinic acid
(DPA)?
A. Degrading the mother cell DNA
B. Forming the thick peptidoglycan cortex
,C. Providing a carbon source for germination
D. Dehydrating the spore and stabilizing proteins
Answer: D
Conceptual Explanation: Dipicolinic acid complexes with calcium ions to dehydrate the
core and protect the DNA and proteins from heat and radiation damage.
3. Which enzyme is responsible for synthesizing a short RNA primer to provide a 3’-OH group
for DNA polymerase III during bacterial DNA replication?
A. Helicase
B. Ligase
C. Topoisomerase
D. Primase
Answer: D
Conceptual Explanation: Primase (an RNA polymerase) creates the RNA primer required
because DNA polymerases cannot initiate synthesis de novo.
4. In the lac operon, what happens to the repressor protein when lactose (allolactose) is
present in the cell?
A. It binds to the promoter to recruit RNA polymerase.
B. It undergoes a conformational change and dissociates from the operator.
C. It binds to the structural genes to prevent translation.
, D. It is degraded by intracellular proteases.
Answer: B
Conceptual Explanation: Allolactose acts as an inducer that binds the repressor, changing
its shape so it can no longer bind to the operator, allowing transcription.
5. Which horizontal gene transfer mechanism requires direct cell-to-cell contact and is often
mediated by a sex pilus?
A. Transformation
B. Conjugation
C. Generalized Transduction
D. Specialized Transduction
Answer: B
Conceptual Explanation: Conjugation involves the transfer of genetic material via a
physical bridge (pilus) between a donor and a recipient cell.
6. Which bacterial growth phase is characterized by a constant rate of division where the
generation time is at its minimum?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log (Exponential) phase
PRACTICE EXAM 2026
1. Which of the following components is unique to the cell wall of Gram-positive bacteria and
functions in cation transport and antigenic specificity?
A. Lipopolysaccharide (LPS)
B. N-acetylmuramic acid
C. Outer membrane protein A (OmpA)
D. Teichoic acids
Answer: D
Conceptual Explanation: Teichoic acids are poly-alcohol phosphates found in Gram-
positive cell walls that help regulate cation movement and provide antigenic variation; LPS
is specific to Gram-negatives.
2. During the process of endospore formation, what is the specific role of dipicolinic acid
(DPA)?
A. Degrading the mother cell DNA
B. Forming the thick peptidoglycan cortex
,C. Providing a carbon source for germination
D. Dehydrating the spore and stabilizing proteins
Answer: D
Conceptual Explanation: Dipicolinic acid complexes with calcium ions to dehydrate the
core and protect the DNA and proteins from heat and radiation damage.
3. Which enzyme is responsible for synthesizing a short RNA primer to provide a 3’-OH group
for DNA polymerase III during bacterial DNA replication?
A. Helicase
B. Ligase
C. Topoisomerase
D. Primase
Answer: D
Conceptual Explanation: Primase (an RNA polymerase) creates the RNA primer required
because DNA polymerases cannot initiate synthesis de novo.
4. In the lac operon, what happens to the repressor protein when lactose (allolactose) is
present in the cell?
A. It binds to the promoter to recruit RNA polymerase.
B. It undergoes a conformational change and dissociates from the operator.
C. It binds to the structural genes to prevent translation.
, D. It is degraded by intracellular proteases.
Answer: B
Conceptual Explanation: Allolactose acts as an inducer that binds the repressor, changing
its shape so it can no longer bind to the operator, allowing transcription.
5. Which horizontal gene transfer mechanism requires direct cell-to-cell contact and is often
mediated by a sex pilus?
A. Transformation
B. Conjugation
C. Generalized Transduction
D. Specialized Transduction
Answer: B
Conceptual Explanation: Conjugation involves the transfer of genetic material via a
physical bridge (pilus) between a donor and a recipient cell.
6. Which bacterial growth phase is characterized by a constant rate of division where the
generation time is at its minimum?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log (Exponential) phase
