ADVANCED MICROBIOLOGY (BIOL 271)
COMPREHENSIVE EXAM
1. Which component of the Gram-positive cell wall is responsible for anchoring the
peptidoglycan to the cytoplasmic membrane?
A. Lipopolysaccharide
B. Periplasm
C. Lipoteichoic acid
D. Porin proteins
Answer: C
Conceptual Explanation: Lipoteichoic acids are linked to the cytoplasmic membrane and
extend through the peptidoglycan layer, providing structural integrity, while teichoic acids
are linked only to the peptidoglycan.
2. In the context of bacterial growth, what occurs during the ‘diauxic shift’?
A. A transition from aerobic to anaerobic respiration
B. The initiation of sporulation due to nutrient exhaustion
C. The rapid increase of mutation rates in the stationary phase
D. A switch between two different carbon sources causing a second lag phase
,Answer: D
Conceptual Explanation: Diauxic growth occurs when a microorganism is provided with
two sugars; it consumes the preferred one first, followed by a lag phase where it
synthesizes enzymes for the second sugar, then consumes the second.
3. Which enzyme is responsible for relieving torsional strain (supercoiling) ahead of the
replication fork in E. coli?
A. DNA Polymerase III
B. Helicase
C. DNA Gyrase (Topoisomerase II)
D. Primase
Answer: C
Conceptual Explanation: DNA Gyrase is a type II topoisomerase that introduces negative
supercoils to neutralize the positive supercoiling caused by helicase during unwinding.
4. The Entner-Doudoroff (ED) pathway is an alternative to glycolysis. Which of the following is
a key intermediate unique to this pathway?
A. Fructose-1,6-bisphosphate
B. 2-keto-3-deoxy-6-phosphogluconate (KDPG)
C. Phosphoenolpyruvate (PEP)
D. Glyceraldehyde-3-phosphate
, Answer: B
Conceptual Explanation: KDPG is the signature intermediate of the ED pathway, which
produces 1 ATP, 1 NADH, and 1 NADPH per glucose, used by some Gram-negative bacteria
like Pseudomonas.
5. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
environment?
A. Conjugation
B. Specialized Transduction
C. Generalized Transduction
D. Transformation
Answer: D
Conceptual Explanation: Transformation is the process by which competent bacteria take
up free DNA fragments from their surroundings.
6. During the lysogenic cycle of a temperate bacteriophage, the integrated viral DNA is
referred to as a:
A. Virion
B. Prophage
C. Capsid
D. Plasmid
COMPREHENSIVE EXAM
1. Which component of the Gram-positive cell wall is responsible for anchoring the
peptidoglycan to the cytoplasmic membrane?
A. Lipopolysaccharide
B. Periplasm
C. Lipoteichoic acid
D. Porin proteins
Answer: C
Conceptual Explanation: Lipoteichoic acids are linked to the cytoplasmic membrane and
extend through the peptidoglycan layer, providing structural integrity, while teichoic acids
are linked only to the peptidoglycan.
2. In the context of bacterial growth, what occurs during the ‘diauxic shift’?
A. A transition from aerobic to anaerobic respiration
B. The initiation of sporulation due to nutrient exhaustion
C. The rapid increase of mutation rates in the stationary phase
D. A switch between two different carbon sources causing a second lag phase
,Answer: D
Conceptual Explanation: Diauxic growth occurs when a microorganism is provided with
two sugars; it consumes the preferred one first, followed by a lag phase where it
synthesizes enzymes for the second sugar, then consumes the second.
3. Which enzyme is responsible for relieving torsional strain (supercoiling) ahead of the
replication fork in E. coli?
A. DNA Polymerase III
B. Helicase
C. DNA Gyrase (Topoisomerase II)
D. Primase
Answer: C
Conceptual Explanation: DNA Gyrase is a type II topoisomerase that introduces negative
supercoils to neutralize the positive supercoiling caused by helicase during unwinding.
4. The Entner-Doudoroff (ED) pathway is an alternative to glycolysis. Which of the following is
a key intermediate unique to this pathway?
A. Fructose-1,6-bisphosphate
B. 2-keto-3-deoxy-6-phosphogluconate (KDPG)
C. Phosphoenolpyruvate (PEP)
D. Glyceraldehyde-3-phosphate
, Answer: B
Conceptual Explanation: KDPG is the signature intermediate of the ED pathway, which
produces 1 ATP, 1 NADH, and 1 NADPH per glucose, used by some Gram-negative bacteria
like Pseudomonas.
5. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
environment?
A. Conjugation
B. Specialized Transduction
C. Generalized Transduction
D. Transformation
Answer: D
Conceptual Explanation: Transformation is the process by which competent bacteria take
up free DNA fragments from their surroundings.
6. During the lysogenic cycle of a temperate bacteriophage, the integrated viral DNA is
referred to as a:
A. Virion
B. Prophage
C. Capsid
D. Plasmid
