BIO 250 Exam 4 V3 | BIO 250 Microbiology | Actual
Q&A with Rationale (BIO250 Exam 4) |
StraighterLine
1. During DNA replication, which enzyme is responsible for unwinding the DNA double helix
at the replication fork?
A. DNA Polymerase I
B. Primase
C. Ligase
D. Helicase
Correct Answer: D
Explanation: Helicase is a critical enzyme that breaks the hydrogen bonds between
complementary base pairs to unzip the DNA molecule. This action creates the replication
fork, allowing other enzymes to access the single-stranded templates. Without helicase
activity, the double helix would remain closed and replication could not proceed.
2. Identify all the components and enzymes required for the process of bacterial DNA
replication. (Select all that apply)
A. DNA Polymerase III
B. DNA Ligase
C. Primase
,D. Helicase
E. Topoisomerase (Gyrase)
F. Reverse Transcriptase
Correct Answer: A, B, C, D, E
Explanation: Bacterial DNA replication requires a coordinated effort from multiple
enzymes including DNA Polymerase III for synthesis and Helicase for unwinding. Primase
is necessary to provide an RNA primer, while Ligase seals the nicks in the sugar-phosphate
backbone, especially on the lagging strand. Reverse transcriptase is not involved in
standard bacterial replication as it is primarily used by retroviruses to convert RNA to
DNA.
3. In the context of the lac operon in Escherichia coli, what occurs when lactose is present and
glucose is absent?
A. The repressor binds to the operator, preventing transcription.
B. Allolactose binds to the repressor, causing it to dissociate from the operator.
C. CAMP levels are low, and the CAP protein remains inactive.
D. Transcription is blocked by the presence of high levels of tryptophan.
Correct Answer: B
Explanation: When lactose is present, it is converted to allolactose, which acts as an
inducer by binding to the repressor protein. This binding changes the conformation of the
, repressor, preventing it from attaching to the operator site. Consequently, RNA polymerase
is free to transcribe the structural genes required for lactose metabolism.
4. Which type of mutation results in the substitution of one amino acid for another in the
resulting protein?
A. Silent mutation
B. Nonsense mutation
C. Missense mutation
D. Frameshift mutation
Correct Answer: C
Explanation: A missense mutation involves a single nucleotide change that alters a codon
so that it specifies a different amino acid. This can lead to changes in the protein’s primary
structure and potentially affect its overall function. In contrast, silent mutations do not
change the amino acid, while nonsense mutations create a premature stop codon.
5. The process by which ‘naked’ DNA is taken up by a competent bacterial cell from the
surrounding environment is known as:
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Q&A with Rationale (BIO250 Exam 4) |
StraighterLine
1. During DNA replication, which enzyme is responsible for unwinding the DNA double helix
at the replication fork?
A. DNA Polymerase I
B. Primase
C. Ligase
D. Helicase
Correct Answer: D
Explanation: Helicase is a critical enzyme that breaks the hydrogen bonds between
complementary base pairs to unzip the DNA molecule. This action creates the replication
fork, allowing other enzymes to access the single-stranded templates. Without helicase
activity, the double helix would remain closed and replication could not proceed.
2. Identify all the components and enzymes required for the process of bacterial DNA
replication. (Select all that apply)
A. DNA Polymerase III
B. DNA Ligase
C. Primase
,D. Helicase
E. Topoisomerase (Gyrase)
F. Reverse Transcriptase
Correct Answer: A, B, C, D, E
Explanation: Bacterial DNA replication requires a coordinated effort from multiple
enzymes including DNA Polymerase III for synthesis and Helicase for unwinding. Primase
is necessary to provide an RNA primer, while Ligase seals the nicks in the sugar-phosphate
backbone, especially on the lagging strand. Reverse transcriptase is not involved in
standard bacterial replication as it is primarily used by retroviruses to convert RNA to
DNA.
3. In the context of the lac operon in Escherichia coli, what occurs when lactose is present and
glucose is absent?
A. The repressor binds to the operator, preventing transcription.
B. Allolactose binds to the repressor, causing it to dissociate from the operator.
C. CAMP levels are low, and the CAP protein remains inactive.
D. Transcription is blocked by the presence of high levels of tryptophan.
Correct Answer: B
Explanation: When lactose is present, it is converted to allolactose, which acts as an
inducer by binding to the repressor protein. This binding changes the conformation of the
, repressor, preventing it from attaching to the operator site. Consequently, RNA polymerase
is free to transcribe the structural genes required for lactose metabolism.
4. Which type of mutation results in the substitution of one amino acid for another in the
resulting protein?
A. Silent mutation
B. Nonsense mutation
C. Missense mutation
D. Frameshift mutation
Correct Answer: C
Explanation: A missense mutation involves a single nucleotide change that alters a codon
so that it specifies a different amino acid. This can lead to changes in the protein’s primary
structure and potentially affect its overall function. In contrast, silent mutations do not
change the amino acid, while nonsense mutations create a premature stop codon.
5. The process by which ‘naked’ DNA is taken up by a competent bacterial cell from the
surrounding environment is known as:
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
