BIO 250 Exam 3 V2 | BIO 250 Microbiology
| Actual Q&A with Rationale (BIO250 Exam
3) | StraighterLine
1. Which of the following enzymes is responsible for unwinding the DNA double helix at the
replication fork during DNA replication?
A. Helicase
B. DNA Polymerase III
C. DNA Ligase
D. Primase
Answer: A
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the strands. This process creates the replication fork where
other enzymes can begin the synthesis of new DNA. Without helicase activity, the double-
stranded DNA would remain coiled and inaccessible for replication.
2. Which of the following are characteristics or types of point mutations? Select all that apply.
A. Silent mutation
B. Thymine dimers
C. Nonsense mutation
D. Missense mutation
,E. Frameshift mutation via insertion
F. Chromosomal translocation
Answer: A, C, D
Rationale: Point mutations refer to changes in a single nucleotide base pair within the DNA
sequence. Silent mutations change the DNA but not the resulting amino acid; missense
mutations change the amino acid; and nonsense mutations create a premature stop codon.
Frameshift mutations and thymine dimers are different categories of genetic alterations
involving multiple bases or structural changes.
3. In the context of the lac operon, what occurs when lactose is present in the environment
and glucose is absent?
A. The repressor binds to the operator, preventing transcription.
B. CAMP levels decrease, leading to low transcription levels.
C. Allolactose binds to the repressor, allowing RNA polymerase to transcribe the genes.
D. The promoter is degraded by nucleases.
Answer: C
Rationale: When lactose is present, it is converted to allolactose, which acts as an inducer
by binding to the repressor protein and changing its shape. This prevents the repressor
from binding to the operator site, thereby clearing the path for RNA polymerase. Since
glucose is absent, cAMP levels are high, which further enhances transcription through the
CAP-cAMP complex.
, 4. Which process involves the transfer of DNA from a donor cell to a recipient cell through a
sex pilus?
A. Transformation
B. Transduction
C. Transposition
D. Conjugation
Answer: D
Rationale: Conjugation is the direct transfer of genetic material between two bacterial
cells that are in physical contact via a pilus. This usually involves the transfer of an F
plasmid from an F+ cell to an F- cell. It is a major mechanism for the spread of antibiotic
resistance in bacterial populations.
5. During the process of transcription, RNA polymerase binds to which specific region of the
DNA?
A. Exon
B. Operator
C. Terminator
D. Promoter
Answer: D
| Actual Q&A with Rationale (BIO250 Exam
3) | StraighterLine
1. Which of the following enzymes is responsible for unwinding the DNA double helix at the
replication fork during DNA replication?
A. Helicase
B. DNA Polymerase III
C. DNA Ligase
D. Primase
Answer: A
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the strands. This process creates the replication fork where
other enzymes can begin the synthesis of new DNA. Without helicase activity, the double-
stranded DNA would remain coiled and inaccessible for replication.
2. Which of the following are characteristics or types of point mutations? Select all that apply.
A. Silent mutation
B. Thymine dimers
C. Nonsense mutation
D. Missense mutation
,E. Frameshift mutation via insertion
F. Chromosomal translocation
Answer: A, C, D
Rationale: Point mutations refer to changes in a single nucleotide base pair within the DNA
sequence. Silent mutations change the DNA but not the resulting amino acid; missense
mutations change the amino acid; and nonsense mutations create a premature stop codon.
Frameshift mutations and thymine dimers are different categories of genetic alterations
involving multiple bases or structural changes.
3. In the context of the lac operon, what occurs when lactose is present in the environment
and glucose is absent?
A. The repressor binds to the operator, preventing transcription.
B. CAMP levels decrease, leading to low transcription levels.
C. Allolactose binds to the repressor, allowing RNA polymerase to transcribe the genes.
D. The promoter is degraded by nucleases.
Answer: C
Rationale: When lactose is present, it is converted to allolactose, which acts as an inducer
by binding to the repressor protein and changing its shape. This prevents the repressor
from binding to the operator site, thereby clearing the path for RNA polymerase. Since
glucose is absent, cAMP levels are high, which further enhances transcription through the
CAP-cAMP complex.
, 4. Which process involves the transfer of DNA from a donor cell to a recipient cell through a
sex pilus?
A. Transformation
B. Transduction
C. Transposition
D. Conjugation
Answer: D
Rationale: Conjugation is the direct transfer of genetic material between two bacterial
cells that are in physical contact via a pilus. This usually involves the transfer of an F
plasmid from an F+ cell to an F- cell. It is a major mechanism for the spread of antibiotic
resistance in bacterial populations.
5. During the process of transcription, RNA polymerase binds to which specific region of the
DNA?
A. Exon
B. Operator
C. Terminator
D. Promoter
Answer: D
