BIO 250 Exam 3 V3 | BIO 250 Microbiology | Actual Q&A with
Rationale (BIO250 Exam 3) | StraighterLine
1. Which of the following processes contribute to genetic diversity in bacterial populations?
Select all that apply.
A. Transformation
B. Conjugation
C. Transduction
D. Spontaneous Mutation
E. Mitosis
F. Binary Fission without errors
Correct Answer: A, B, C, D
Explanation: Genetic diversity in bacteria is primarily driven by horizontal gene transfer
mechanisms and spontaneous mutations. Horizontal gene transfer includes transformation,
transduction, and conjugation, which allow for the acquisition of new alleles from other
cells or the environment. Binary fission is a form of asexual reproduction that produces
clones, and mitosis does not occur in prokaryotic cells.
2. Which enzyme is responsible for synthesizing a short RNA sequence to initiate DNA
replication?
A. Primase
B. DNA Polymerase I
C. Helicase
D. Ligase
Correct Answer: A
Explanation: Primase is a type of RNA polymerase that creates an RNA primer, which
provides the 3’-OH group necessary for DNA polymerase to begin synthesis. Without this
primer, DNA polymerase III would be unable to initiate the addition of nucleotides. Once
the primer is in place, DNA synthesis can proceed in the 5’ to 3’ direction.
3. In DNA replication, which strand is synthesized continuously toward the replication fork?
A. Lagging strand
B. Template strand
C. Leading strand
,D. Okazaki strand
Correct Answer: C
Explanation: The leading strand is synthesized in the same direction as the movement of
the replication fork, allowing for continuous addition of nucleotides. In contrast, the lagging
strand is synthesized in short fragments known as Okazaki fragments because it moves
away from the fork. This directional synthesis is dictated by the antiparallel nature of DNA
and the 5’ to 3’ activity of DNA polymerase.
4. The process by which the information in a DNA template is used to guide the synthesis of
an RNA molecule is called:
A. Translation
B. Replication
C. Transformation
D. Transcription
Correct Answer: D
Explanation: Transcription is the first step of gene expression where a specific segment of
DNA is copied into RNA by the enzyme RNA polymerase. This process occurs in the
nucleoid region of bacteria or the nucleus of eukaryotes. The resulting RNA, often mRNA,
then carries the genetic code to the ribosome for protein synthesis.
5. Which of the following are components of a DNA nucleotide? Select all that apply.
A. Deoxyribose sugar
B. Phosphate group
C. Nitrogenous base (A, T, C, or G)
D. Ribose sugar
E. Uracil
Correct Answer: A, B, C
Explanation: A DNA nucleotide consists of three fundamental parts: a five-carbon
deoxyribose sugar, a phosphate group, and one of four nitrogenous bases. Ribose and uracil
are specific to RNA nucleotides and are not found in standard DNA structures. The
arrangement of these components forms the backbone and the genetic code of the double
helix.
6. The region of an operon where RNA polymerase binds to initiate transcription is the:
A. Operator
B. Promoter
, C. Structural gene
D. Regulator
Correct Answer: B
Explanation: The promoter is a specific DNA sequence that signals the start of a gene and
serves as the binding site for RNA polymerase. Its sequence determines the affinity for the
enzyme and thus influences the frequency of transcription. The operator, conversely, acts
as a switch that can be blocked by repressor proteins.
7. A mutation that changes a single amino acid in a protein sequence is known as a:
A. Silent mutation
B. Missense mutation
C. Nonsense mutation
D. Frameshift mutation
Correct Answer: B
Explanation: A missense mutation results from a point mutation that causes a different
amino acid to be incorporated into the resulting polypeptide. This change can vary in its
effect on protein function depending on the chemical properties of the new amino acid. If
the change occurs in a critical region like an active site, it can significantly alter the
organism’s phenotype.
8. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: A
Explanation: Transformation is the process by which competent bacterial cells take up
free DNA fragments released by dead or lysed cells in the environment. This was famously
demonstrated by Frederick Griffith in his experiments with Streptococcus pneumoniae.
Once inside, the foreign DNA can be integrated into the host genome through
recombination.
9. Which enzyme is responsible for sealing the nicks between DNA fragments, such as Okazaki
fragments, by forming covalent phosphodiester bonds?
A. DNA Ligase
Rationale (BIO250 Exam 3) | StraighterLine
1. Which of the following processes contribute to genetic diversity in bacterial populations?
Select all that apply.
A. Transformation
B. Conjugation
C. Transduction
D. Spontaneous Mutation
E. Mitosis
F. Binary Fission without errors
Correct Answer: A, B, C, D
Explanation: Genetic diversity in bacteria is primarily driven by horizontal gene transfer
mechanisms and spontaneous mutations. Horizontal gene transfer includes transformation,
transduction, and conjugation, which allow for the acquisition of new alleles from other
cells or the environment. Binary fission is a form of asexual reproduction that produces
clones, and mitosis does not occur in prokaryotic cells.
2. Which enzyme is responsible for synthesizing a short RNA sequence to initiate DNA
replication?
A. Primase
B. DNA Polymerase I
C. Helicase
D. Ligase
Correct Answer: A
Explanation: Primase is a type of RNA polymerase that creates an RNA primer, which
provides the 3’-OH group necessary for DNA polymerase to begin synthesis. Without this
primer, DNA polymerase III would be unable to initiate the addition of nucleotides. Once
the primer is in place, DNA synthesis can proceed in the 5’ to 3’ direction.
3. In DNA replication, which strand is synthesized continuously toward the replication fork?
A. Lagging strand
B. Template strand
C. Leading strand
,D. Okazaki strand
Correct Answer: C
Explanation: The leading strand is synthesized in the same direction as the movement of
the replication fork, allowing for continuous addition of nucleotides. In contrast, the lagging
strand is synthesized in short fragments known as Okazaki fragments because it moves
away from the fork. This directional synthesis is dictated by the antiparallel nature of DNA
and the 5’ to 3’ activity of DNA polymerase.
4. The process by which the information in a DNA template is used to guide the synthesis of
an RNA molecule is called:
A. Translation
B. Replication
C. Transformation
D. Transcription
Correct Answer: D
Explanation: Transcription is the first step of gene expression where a specific segment of
DNA is copied into RNA by the enzyme RNA polymerase. This process occurs in the
nucleoid region of bacteria or the nucleus of eukaryotes. The resulting RNA, often mRNA,
then carries the genetic code to the ribosome for protein synthesis.
5. Which of the following are components of a DNA nucleotide? Select all that apply.
A. Deoxyribose sugar
B. Phosphate group
C. Nitrogenous base (A, T, C, or G)
D. Ribose sugar
E. Uracil
Correct Answer: A, B, C
Explanation: A DNA nucleotide consists of three fundamental parts: a five-carbon
deoxyribose sugar, a phosphate group, and one of four nitrogenous bases. Ribose and uracil
are specific to RNA nucleotides and are not found in standard DNA structures. The
arrangement of these components forms the backbone and the genetic code of the double
helix.
6. The region of an operon where RNA polymerase binds to initiate transcription is the:
A. Operator
B. Promoter
, C. Structural gene
D. Regulator
Correct Answer: B
Explanation: The promoter is a specific DNA sequence that signals the start of a gene and
serves as the binding site for RNA polymerase. Its sequence determines the affinity for the
enzyme and thus influences the frequency of transcription. The operator, conversely, acts
as a switch that can be blocked by repressor proteins.
7. A mutation that changes a single amino acid in a protein sequence is known as a:
A. Silent mutation
B. Missense mutation
C. Nonsense mutation
D. Frameshift mutation
Correct Answer: B
Explanation: A missense mutation results from a point mutation that causes a different
amino acid to be incorporated into the resulting polypeptide. This change can vary in its
effect on protein function depending on the chemical properties of the new amino acid. If
the change occurs in a critical region like an active site, it can significantly alter the
organism’s phenotype.
8. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: A
Explanation: Transformation is the process by which competent bacterial cells take up
free DNA fragments released by dead or lysed cells in the environment. This was famously
demonstrated by Frederick Griffith in his experiments with Streptococcus pneumoniae.
Once inside, the foreign DNA can be integrated into the host genome through
recombination.
9. Which enzyme is responsible for sealing the nicks between DNA fragments, such as Okazaki
fragments, by forming covalent phosphodiester bonds?
A. DNA Ligase
