BIOL 3200 Final Exam Actual Exam V2 | BIOL 3200 General
Microbiology (BIOL 3200 Final Exam) | Auburn University
1. Which of the following best describes the mechanism of action for the beta-lactam
antibiotic Penicillin?
A. It inhibits the 30S ribosomal subunit to prevent protein synthesis.
B. It binds to transpeptidase enzymes to prevent peptidoglycan cross-linking.
C. It disrupts the cytoplasmic membrane by increasing permeability.
D. It inhibits DNA gyrase, preventing the relief of supercoiling.
Answer: B
Rationale: Penicillin acts as a competitive inhibitor for the enzyme transpeptidase, which
is responsible for forming peptide cross-links in the bacterial cell wall. By blocking this
step, the cell wall becomes structurally weak, leading to osmotic lysis during cell growth.
This mechanism is specifically effective against actively growing bacteria that are
synthesizing new peptidoglycan.
2. In the process of bacterial conjugation involving an Hfr strain, what is typically transferred
to the recipient cell?
A. A complete copy of the F-plasmid only.
B. Naked DNA fragments from the environment.
C. Chromosomal DNA starting from the origin of transfer (oriT).
D. Bacteriophage DNA containing host genes.
Answer: C
Rationale: High Frequency of Recombination (Hfr) strains have the F-plasmid integrated
into their bacterial chromosome. During conjugation, the transfer begins at the oriT site
within the plasmid sequence and proceeds to include the adjacent chromosomal genes.
Because the entire chromosome is rarely transferred before the pilus breaks, the recipient
usually remains F-negative but gains new genetic alleles.
3. Which metabolic pathway produces the highest net yield of ATP per molecule of glucose
oxidized?
A. Lactic acid fermentation
B. Anaerobic respiration using nitrate as an electron acceptor
C. Aerobic respiration
D. Entner-Doudoroff pathway
,Answer: C
Rationale: Aerobic respiration utilizes oxygen as the terminal electron acceptor in the
electron transport chain, which provides the greatest reduction potential difference. This
allows for the generation of approximately 38 ATP molecules through both substrate-level
and oxidative phosphorylation. In contrast, fermentation and anaerobic respiration yield
significantly less energy due to incomplete oxidation or less efficient electron acceptors.
4. A Gram-negative bacterium is characterized by the presence of which of the following
components?
A. A thick layer of peptidoglycan and teichoic acids.
B. A cell wall composed primarily of pseudomurein.
C. A thin layer of peptidoglycan and an outer membrane containing Lipopolysaccharide
(LPS).
D. A single plasma membrane with no cell wall.
Answer: C
Rationale: Gram-negative bacteria possess a complex cell envelope consisting of a thin
peptidoglycan layer located within the periplasmic space between the inner and outer
membranes. The outer membrane contains specialized molecules such as
Lipopolysaccharide (LPS), which acts as an endotoxin. This structural configuration
contributes to the bacteria’s resistance to certain antibiotics and host immune responses.
5. Which enzyme is responsible for synthesizing a short RNA primer during bacterial DNA
replication?
A. DNA Polymerase I
B. Primase
C. DNA Polymerase III
D. Helicase
Answer: B
Rationale: Primase is a specialized RNA polymerase that synthesizes a short RNA primer
complementary to the DNA template. This primer provides the essential 3’-OH group
required by DNA Polymerase III to begin adding deoxyribonucleotides. On the lagging
strand, multiple primers are synthesized to facilitate the formation of Okazaki fragments.
6. Which of the following is an example of a chemolithoautotroph?
A. Escherichia coli using glucose for energy and carbon.
B. Cyanobacteria using light for energy and CO2 for carbon.
C. Nitrobacter using nitrite for energy and CO2 for carbon.
, D. Staphylococcus aureus using proteins for carbon and energy.
Answer: C
Rationale: Chemolithoautotrophs derive their energy from the oxidation of inorganic
chemicals and use carbon dioxide as their sole carbon source. Nitrobacter is a classic
example as it oxidizes nitrite to nitrate to generate ATP via an electron transport chain.
This metabolic strategy is vital for global nitrogen cycling in various ecosystems.
7. In the lac operon of E. coli, what happens when both glucose and lactose are present in the
environment?
A. High levels of transcription occur due to the presence of lactose.
B. Transcription is inhibited because cAMP levels are low, preventing CAP binding.
C. The repressor remains bound to the operator regardless of lactose.
D. Tryptophan acts as a corepressor to shut down the operon.
Answer: B
Rationale: When glucose is present, the cell suppresses the use of alternative carbon
sources through catabolite repression. Glucose inhibits the enzyme adenylate cyclase,
leading to low levels of cyclic AMP (cAMP). Since cAMP is required for the Catabolite
Activator Protein (CAP) to bind and recruit RNA polymerase, the lac operon is transcribed
only at very low basal levels even if lactose is present.
8. Which type of mutation results in a premature stop codon and a truncated protein?
A. Missense mutation
B. Silent mutation
C. Frameshift mutation
D. Nonsense mutation
Answer: D
Rationale: A nonsense mutation is a point mutation in a sequence of DNA that results in a
premature stop codon in the transcribed mRNA. This leads to the early termination of
translation, producing a shortened and usually non-functional protein. This is distinct from
a missense mutation, which merely changes one amino acid to another.
9. What is the primary function of the bacterial capsule?
A. Facilitating movement through liquid media.
B. Serving as the primary site for oxidative phosphorylation.
C. Regulating the transport of ions across the membrane.
D. Protecting the cell from phagocytosis by host immune cells.
Microbiology (BIOL 3200 Final Exam) | Auburn University
1. Which of the following best describes the mechanism of action for the beta-lactam
antibiotic Penicillin?
A. It inhibits the 30S ribosomal subunit to prevent protein synthesis.
B. It binds to transpeptidase enzymes to prevent peptidoglycan cross-linking.
C. It disrupts the cytoplasmic membrane by increasing permeability.
D. It inhibits DNA gyrase, preventing the relief of supercoiling.
Answer: B
Rationale: Penicillin acts as a competitive inhibitor for the enzyme transpeptidase, which
is responsible for forming peptide cross-links in the bacterial cell wall. By blocking this
step, the cell wall becomes structurally weak, leading to osmotic lysis during cell growth.
This mechanism is specifically effective against actively growing bacteria that are
synthesizing new peptidoglycan.
2. In the process of bacterial conjugation involving an Hfr strain, what is typically transferred
to the recipient cell?
A. A complete copy of the F-plasmid only.
B. Naked DNA fragments from the environment.
C. Chromosomal DNA starting from the origin of transfer (oriT).
D. Bacteriophage DNA containing host genes.
Answer: C
Rationale: High Frequency of Recombination (Hfr) strains have the F-plasmid integrated
into their bacterial chromosome. During conjugation, the transfer begins at the oriT site
within the plasmid sequence and proceeds to include the adjacent chromosomal genes.
Because the entire chromosome is rarely transferred before the pilus breaks, the recipient
usually remains F-negative but gains new genetic alleles.
3. Which metabolic pathway produces the highest net yield of ATP per molecule of glucose
oxidized?
A. Lactic acid fermentation
B. Anaerobic respiration using nitrate as an electron acceptor
C. Aerobic respiration
D. Entner-Doudoroff pathway
,Answer: C
Rationale: Aerobic respiration utilizes oxygen as the terminal electron acceptor in the
electron transport chain, which provides the greatest reduction potential difference. This
allows for the generation of approximately 38 ATP molecules through both substrate-level
and oxidative phosphorylation. In contrast, fermentation and anaerobic respiration yield
significantly less energy due to incomplete oxidation or less efficient electron acceptors.
4. A Gram-negative bacterium is characterized by the presence of which of the following
components?
A. A thick layer of peptidoglycan and teichoic acids.
B. A cell wall composed primarily of pseudomurein.
C. A thin layer of peptidoglycan and an outer membrane containing Lipopolysaccharide
(LPS).
D. A single plasma membrane with no cell wall.
Answer: C
Rationale: Gram-negative bacteria possess a complex cell envelope consisting of a thin
peptidoglycan layer located within the periplasmic space between the inner and outer
membranes. The outer membrane contains specialized molecules such as
Lipopolysaccharide (LPS), which acts as an endotoxin. This structural configuration
contributes to the bacteria’s resistance to certain antibiotics and host immune responses.
5. Which enzyme is responsible for synthesizing a short RNA primer during bacterial DNA
replication?
A. DNA Polymerase I
B. Primase
C. DNA Polymerase III
D. Helicase
Answer: B
Rationale: Primase is a specialized RNA polymerase that synthesizes a short RNA primer
complementary to the DNA template. This primer provides the essential 3’-OH group
required by DNA Polymerase III to begin adding deoxyribonucleotides. On the lagging
strand, multiple primers are synthesized to facilitate the formation of Okazaki fragments.
6. Which of the following is an example of a chemolithoautotroph?
A. Escherichia coli using glucose for energy and carbon.
B. Cyanobacteria using light for energy and CO2 for carbon.
C. Nitrobacter using nitrite for energy and CO2 for carbon.
, D. Staphylococcus aureus using proteins for carbon and energy.
Answer: C
Rationale: Chemolithoautotrophs derive their energy from the oxidation of inorganic
chemicals and use carbon dioxide as their sole carbon source. Nitrobacter is a classic
example as it oxidizes nitrite to nitrate to generate ATP via an electron transport chain.
This metabolic strategy is vital for global nitrogen cycling in various ecosystems.
7. In the lac operon of E. coli, what happens when both glucose and lactose are present in the
environment?
A. High levels of transcription occur due to the presence of lactose.
B. Transcription is inhibited because cAMP levels are low, preventing CAP binding.
C. The repressor remains bound to the operator regardless of lactose.
D. Tryptophan acts as a corepressor to shut down the operon.
Answer: B
Rationale: When glucose is present, the cell suppresses the use of alternative carbon
sources through catabolite repression. Glucose inhibits the enzyme adenylate cyclase,
leading to low levels of cyclic AMP (cAMP). Since cAMP is required for the Catabolite
Activator Protein (CAP) to bind and recruit RNA polymerase, the lac operon is transcribed
only at very low basal levels even if lactose is present.
8. Which type of mutation results in a premature stop codon and a truncated protein?
A. Missense mutation
B. Silent mutation
C. Frameshift mutation
D. Nonsense mutation
Answer: D
Rationale: A nonsense mutation is a point mutation in a sequence of DNA that results in a
premature stop codon in the transcribed mRNA. This leads to the early termination of
translation, producing a shortened and usually non-functional protein. This is distinct from
a missense mutation, which merely changes one amino acid to another.
9. What is the primary function of the bacterial capsule?
A. Facilitating movement through liquid media.
B. Serving as the primary site for oxidative phosphorylation.
C. Regulating the transport of ions across the membrane.
D. Protecting the cell from phagocytosis by host immune cells.
