BIO 250 Exam 4 V1 | BIO 250 Microbiology | Actual
Q&A with Rationale (BIO250 Exam 4) |
StraighterLine
1. During DNA replication, which enzyme is responsible for adding bases to the new DNA
chain and proofreading the chain for mistakes?
A. Helicase
B. DNA Ligase
C. DNA Polymerase III
D. Gyrase
Correct Answer: C
Explanation: DNA Polymerase III is the primary enzyme involved in the synthesis of the
new DNA strand by adding nucleotides in a 5’ to 3’ direction. It also possesses a
proofreading function that allows it to excise incorrectly paired bases. Other enzymes like
helicase and ligase serve to unwind the DNA and seal nicks, respectively.
2. Which of the following are considered physical methods of microbial control? Select all
that apply.
A. Ionizing radiation
B. Moist heat
C. Ethylene oxide gas
,D. Desiccation
E. Cold temperatures
F. Phenolic compounds
Correct Answer: A, B, D, E
Explanation: Physical methods of control involve environmental changes such as
temperature, radiation, and pressure rather than chemical reactions. Moist heat, ionizing
radiation, desiccation, and cold are all classified as physical agents. In contrast, ethylene
oxide and phenolics are chemical agents used for disinfection or sterilization.
3. A mutation that changes a normal codon to a stop codon is referred to as a:
A. Silent mutation
B. Missense mutation
C. Back-mutation
D. Nonsense mutation
Correct Answer: D
Explanation: A nonsense mutation results in the premature termination of protein
synthesis by changing a coding triplet into a stop codon. This typically leads to a
nonfunctional protein product because the polypeptide chain is incomplete. Missense
mutations, by comparison, result in a different amino acid being incorporated into the
protein.
, 4. The lactose (lac) operon is usually in the ‘off’ position and is activated by a/an _______
molecule.
A. Corepressor
B. Repressor
C. Inducer
D. Promoter
Correct Answer: C
Explanation: The lac operon is an inducible operon that is typically repressed by a
repressor protein binding to the operator. When lactose is present, it is converted to
allolactose, which acts as an inducer by binding to the repressor and releasing it from the
operator. This allows RNA polymerase to transcribe the structural genes needed for lactose
metabolism.
5. Which process involves the transfer of DNA from a donor to a recipient cell via a
bacteriophage?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: B
Q&A with Rationale (BIO250 Exam 4) |
StraighterLine
1. During DNA replication, which enzyme is responsible for adding bases to the new DNA
chain and proofreading the chain for mistakes?
A. Helicase
B. DNA Ligase
C. DNA Polymerase III
D. Gyrase
Correct Answer: C
Explanation: DNA Polymerase III is the primary enzyme involved in the synthesis of the
new DNA strand by adding nucleotides in a 5’ to 3’ direction. It also possesses a
proofreading function that allows it to excise incorrectly paired bases. Other enzymes like
helicase and ligase serve to unwind the DNA and seal nicks, respectively.
2. Which of the following are considered physical methods of microbial control? Select all
that apply.
A. Ionizing radiation
B. Moist heat
C. Ethylene oxide gas
,D. Desiccation
E. Cold temperatures
F. Phenolic compounds
Correct Answer: A, B, D, E
Explanation: Physical methods of control involve environmental changes such as
temperature, radiation, and pressure rather than chemical reactions. Moist heat, ionizing
radiation, desiccation, and cold are all classified as physical agents. In contrast, ethylene
oxide and phenolics are chemical agents used for disinfection or sterilization.
3. A mutation that changes a normal codon to a stop codon is referred to as a:
A. Silent mutation
B. Missense mutation
C. Back-mutation
D. Nonsense mutation
Correct Answer: D
Explanation: A nonsense mutation results in the premature termination of protein
synthesis by changing a coding triplet into a stop codon. This typically leads to a
nonfunctional protein product because the polypeptide chain is incomplete. Missense
mutations, by comparison, result in a different amino acid being incorporated into the
protein.
, 4. The lactose (lac) operon is usually in the ‘off’ position and is activated by a/an _______
molecule.
A. Corepressor
B. Repressor
C. Inducer
D. Promoter
Correct Answer: C
Explanation: The lac operon is an inducible operon that is typically repressed by a
repressor protein binding to the operator. When lactose is present, it is converted to
allolactose, which acts as an inducer by binding to the repressor and releasing it from the
operator. This allows RNA polymerase to transcribe the structural genes needed for lactose
metabolism.
5. Which process involves the transfer of DNA from a donor to a recipient cell via a
bacteriophage?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: B
