BIOD 171 | BIOD 171 Microbiology Module 7 Exam
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which term describes the ability of an antimicrobial drug to harm a microorganism
without causing significant damage to the host?
A. Bacteriostatic action
B. Selective toxicity
C. Broad-spectrum activity
D. Synergistic effect
Correct Answer: B
Expert Explanation: Selective toxicity is the central principle of antimicrobial
chemotherapy that targets unique microbial structures. This approach ensures that
the drug effectively kills the pathogen while remaining safe for the patient. For
instance, antibiotics often target bacterial cell walls which are absent in human cells.
Without this specificity, the treatment would be as harmful to the host as it is to the
microbe. It is the primary factor used to calculate the safety margin of a clinical
drug.
2. Antibiotics that inhibit the growth of bacteria but do not directly kill them are
classified as:
A. Narrow-spectrum
,B. Bactericidal
C. Lytic agents
D. Bacteriostatic
Correct Answer: D
Expert Explanation: Bacteriostatic drugs function by preventing the reproduction
and growth of bacterial populations. This allows the host’s immune system to
eventually recognize and clear the immobilized infection. Common examples
include tetracyclines and sulfonamides which inhibit protein or folic acid synthesis.
In contrast, bactericidal agents directly cause cell death through mechanisms like
cell wall lysis. Choosing between these types depends on the patient’s immune
status and the severity of the infection.
3. What is the primary mechanism of action for beta-lactam antibiotics like penicillin?
A. Disruption of the plasma membrane
B. Inhibition of cell wall synthesis
C. Inhibition of protein synthesis
D. Interference with DNA replication
Correct Answer: B
,Expert Explanation: Beta-lactam antibiotics work by binding to penicillin-binding
proteins involved in peptidoglycan synthesis. This interference prevents the proper
cross-linking of the bacterial cell wall during growth. As the wall weakens, the
internal osmotic pressure causes the bacterial cell to burst or lyse. Because human
cells do not possess peptidoglycan, these drugs exhibit excellent selective toxicity.
This mechanism is most effective against actively dividing Gram-positive bacteria.
4. Which of the following describes the function of aminoglycosides in treating
bacterial infections?
A. They bind to the 30S ribosomal subunit to inhibit protein synthesis
B. They inhibit RNA polymerase activity
C. They disrupt the outer membrane of Gram-negative cells
D. They block the synthesis of folic acid
Correct Answer: A
Expert Explanation: Aminoglycosides are potent antibiotics that target the
bacterial translation process. By binding specifically to the 30S subunit of the
ribosome, they cause mRNA to be misread. This leads to the production of faulty
proteins that can damage the bacterial cell membrane. While effective against many
Gram-negative rods, they can have side effects like nephrotoxicity in the host. Their
, action is typically bactericidal due to the irreversible nature of the ribosomal
binding.
5. Sulfonamides (sulfa drugs) act as structural analogs of which molecule to inhibit
folic acid synthesis?
A. Para-aminobenzoic acid (PABA)
B. Peptidoglycan
C. Adenosine triphosphate (ATP)
D. Deoxyribonucleic acid (DNA)
Correct Answer: A
Expert Explanation: Sulfonamides function through competitive inhibition by
mimicking the structure of PABA. Bacteria require PABA to synthesize dihydrofolic
acid, which is a precursor for nucleic acids. By occupying the enzyme’s active site,
sulfa drugs prevent the production of essential DNA and RNA building blocks.
Humans are unaffected by this because they obtain folic acid from their diet rather
than synthesizing it. This pathway demonstrates a classic example of metabolic
antagonism in antimicrobial therapy.
6. Fluoroquinolones, such as ciprofloxacin, are effective because they inhibit which
bacterial enzyme?
A. Beta-lactamase
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which term describes the ability of an antimicrobial drug to harm a microorganism
without causing significant damage to the host?
A. Bacteriostatic action
B. Selective toxicity
C. Broad-spectrum activity
D. Synergistic effect
Correct Answer: B
Expert Explanation: Selective toxicity is the central principle of antimicrobial
chemotherapy that targets unique microbial structures. This approach ensures that
the drug effectively kills the pathogen while remaining safe for the patient. For
instance, antibiotics often target bacterial cell walls which are absent in human cells.
Without this specificity, the treatment would be as harmful to the host as it is to the
microbe. It is the primary factor used to calculate the safety margin of a clinical
drug.
2. Antibiotics that inhibit the growth of bacteria but do not directly kill them are
classified as:
A. Narrow-spectrum
,B. Bactericidal
C. Lytic agents
D. Bacteriostatic
Correct Answer: D
Expert Explanation: Bacteriostatic drugs function by preventing the reproduction
and growth of bacterial populations. This allows the host’s immune system to
eventually recognize and clear the immobilized infection. Common examples
include tetracyclines and sulfonamides which inhibit protein or folic acid synthesis.
In contrast, bactericidal agents directly cause cell death through mechanisms like
cell wall lysis. Choosing between these types depends on the patient’s immune
status and the severity of the infection.
3. What is the primary mechanism of action for beta-lactam antibiotics like penicillin?
A. Disruption of the plasma membrane
B. Inhibition of cell wall synthesis
C. Inhibition of protein synthesis
D. Interference with DNA replication
Correct Answer: B
,Expert Explanation: Beta-lactam antibiotics work by binding to penicillin-binding
proteins involved in peptidoglycan synthesis. This interference prevents the proper
cross-linking of the bacterial cell wall during growth. As the wall weakens, the
internal osmotic pressure causes the bacterial cell to burst or lyse. Because human
cells do not possess peptidoglycan, these drugs exhibit excellent selective toxicity.
This mechanism is most effective against actively dividing Gram-positive bacteria.
4. Which of the following describes the function of aminoglycosides in treating
bacterial infections?
A. They bind to the 30S ribosomal subunit to inhibit protein synthesis
B. They inhibit RNA polymerase activity
C. They disrupt the outer membrane of Gram-negative cells
D. They block the synthesis of folic acid
Correct Answer: A
Expert Explanation: Aminoglycosides are potent antibiotics that target the
bacterial translation process. By binding specifically to the 30S subunit of the
ribosome, they cause mRNA to be misread. This leads to the production of faulty
proteins that can damage the bacterial cell membrane. While effective against many
Gram-negative rods, they can have side effects like nephrotoxicity in the host. Their
, action is typically bactericidal due to the irreversible nature of the ribosomal
binding.
5. Sulfonamides (sulfa drugs) act as structural analogs of which molecule to inhibit
folic acid synthesis?
A. Para-aminobenzoic acid (PABA)
B. Peptidoglycan
C. Adenosine triphosphate (ATP)
D. Deoxyribonucleic acid (DNA)
Correct Answer: A
Expert Explanation: Sulfonamides function through competitive inhibition by
mimicking the structure of PABA. Bacteria require PABA to synthesize dihydrofolic
acid, which is a precursor for nucleic acids. By occupying the enzyme’s active site,
sulfa drugs prevent the production of essential DNA and RNA building blocks.
Humans are unaffected by this because they obtain folic acid from their diet rather
than synthesizing it. This pathway demonstrates a classic example of metabolic
antagonism in antimicrobial therapy.
6. Fluoroquinolones, such as ciprofloxacin, are effective because they inhibit which
bacterial enzyme?
A. Beta-lactamase
