BIO 250 Exam 3 V3 | BIO 250 Microbiology
| Actual Q&A with Rationale (BIO250 Exam
3) | StraighterLine
1. During DNA replication, which enzyme is responsible for synthesizing the new DNA strand
by adding nucleotides in a 5’ to 3’ direction?
A. DNA Helicase
B. DNA Polymerase III
C. DNA Primase
D. DNA Ligase
Answer: B
Rationale: DNA Polymerase III is the primary enzyme responsible for the synthesis of the
new DNA strand during replication. It adds deoxyribonucleotides to the 3’ end of the
growing chain, necessitating a 5’ to 3’ directionality. This enzyme also possesses
proofreading capabilities to ensure high fidelity during the replication process.
2. Identify the mechanisms of horizontal gene transfer commonly observed in bacterial
populations. (Select all that apply)
A. Transformation
B. Transduction
C. Conjugation
,D. Binary Fission
E. Mitosis
F. Translation
Answer: A, B, C
Rationale: Transformation, transduction, and conjugation are the three primary methods
by which bacteria exchange genetic material horizontally. Transformation involves the
uptake of naked DNA from the environment, while transduction is mediated by
bacteriophages. Conjugation requires direct cell-to-cell contact via a pilus to transfer
plasmid DNA.
3. In the context of the lac operon, what occurs when lactose is present and glucose is absent
in the environment?
A. The repressor remains bound to the operator, preventing transcription.
B. The repressor is inactivated, and cAMP levels are high, leading to high levels of
transcription.
C. The promoter is degraded by enzymes to prevent waste.
D. Transcription occurs at a basal level because CAP is inactive.
Answer: B
Rationale: When lactose is present, it is converted to allolactose which binds to and
inactivates the repressor. The absence of glucose leads to high levels of cAMP, which binds
, to the Catabolite Activator Protein (CAP), facilitating high-level transcription of the
structural genes. This dual-control mechanism ensures that the cell preferentially uses the
most efficient energy source available.
4. Which type of mutation results from the insertion or deletion of one or two nucleotides,
leading to a shift in the reading frame?
A. Frameshift mutation
B. Silent mutation
C. Point mutation
D. Missense mutation
Answer: A
Rationale: A frameshift mutation occurs when the number of inserted or deleted
nucleotides is not a multiple of three. This alters the reading frame of the mRNA during
translation, typically resulting in a completely different amino acid sequence. Such
mutations often lead to a premature stop codon, rendering the resulting protein
nonfunctional.
5. The process of transcription involves the synthesis of RNA from a DNA template. Which
enzyme is primarily responsible for this process in prokaryotes?
A. DNA Polymerase I
B. Peptidyl Transferase
C. Reverse Transcriptase
| Actual Q&A with Rationale (BIO250 Exam
3) | StraighterLine
1. During DNA replication, which enzyme is responsible for synthesizing the new DNA strand
by adding nucleotides in a 5’ to 3’ direction?
A. DNA Helicase
B. DNA Polymerase III
C. DNA Primase
D. DNA Ligase
Answer: B
Rationale: DNA Polymerase III is the primary enzyme responsible for the synthesis of the
new DNA strand during replication. It adds deoxyribonucleotides to the 3’ end of the
growing chain, necessitating a 5’ to 3’ directionality. This enzyme also possesses
proofreading capabilities to ensure high fidelity during the replication process.
2. Identify the mechanisms of horizontal gene transfer commonly observed in bacterial
populations. (Select all that apply)
A. Transformation
B. Transduction
C. Conjugation
,D. Binary Fission
E. Mitosis
F. Translation
Answer: A, B, C
Rationale: Transformation, transduction, and conjugation are the three primary methods
by which bacteria exchange genetic material horizontally. Transformation involves the
uptake of naked DNA from the environment, while transduction is mediated by
bacteriophages. Conjugation requires direct cell-to-cell contact via a pilus to transfer
plasmid DNA.
3. In the context of the lac operon, what occurs when lactose is present and glucose is absent
in the environment?
A. The repressor remains bound to the operator, preventing transcription.
B. The repressor is inactivated, and cAMP levels are high, leading to high levels of
transcription.
C. The promoter is degraded by enzymes to prevent waste.
D. Transcription occurs at a basal level because CAP is inactive.
Answer: B
Rationale: When lactose is present, it is converted to allolactose which binds to and
inactivates the repressor. The absence of glucose leads to high levels of cAMP, which binds
, to the Catabolite Activator Protein (CAP), facilitating high-level transcription of the
structural genes. This dual-control mechanism ensures that the cell preferentially uses the
most efficient energy source available.
4. Which type of mutation results from the insertion or deletion of one or two nucleotides,
leading to a shift in the reading frame?
A. Frameshift mutation
B. Silent mutation
C. Point mutation
D. Missense mutation
Answer: A
Rationale: A frameshift mutation occurs when the number of inserted or deleted
nucleotides is not a multiple of three. This alters the reading frame of the mRNA during
translation, typically resulting in a completely different amino acid sequence. Such
mutations often lead to a premature stop codon, rendering the resulting protein
nonfunctional.
5. The process of transcription involves the synthesis of RNA from a DNA template. Which
enzyme is primarily responsible for this process in prokaryotes?
A. DNA Polymerase I
B. Peptidyl Transferase
C. Reverse Transcriptase
