BIO 250 Exam 3 V3 | BIO 250 Microbiology | Actual
Q&A with Rationale (BIO250 Exam 3) |
StraighterLine
1. Which enzyme is responsible for synthesizing a short RNA primer to provide a 3’-OH group
for DNA polymerase III to begin DNA synthesis?
A. DNA Ligase
B. Gyrase
C. Helicase
D. Primase
Correct Answer: D
Explanation: Primase is a specialized RNA polymerase that synthesizes a short RNA
primer required for DNA replication. DNA polymerase III cannot initiate synthesis on a
bare template and requires the free 3’-OH group provided by this primer. Once the primer
is in place, DNA polymerase III can extend the new DNA strand in the 5’ to 3’ direction.
2. Select all that apply: Which of the following are recognized mechanisms of horizontal gene
transfer (HGT) in prokaryotic organisms?
A. Conjugation
B. Transformation
C. Binary Fission
,D. Transduction
E. Transposition via transposons
F. Mitotic Division
Correct Answer: A, B, D, E
Explanation: Horizontal gene transfer involves the movement of genetic material between
non-parental cells through processes like conjugation, transformation, and transduction.
Conjugation requires direct cell-to-cell contact, transformation involves the uptake of
naked DNA, and transduction is mediated by bacteriophages. Transposition involves
jumping genes that can move between the chromosome and plasmids, whereas binary
fission and mitosis are forms of vertical transmission.
3. In the context of the lac operon, what occurs when lactose is present in the environment
but glucose is absent?
A. The repressor remains bound to the operator, preventing transcription.
B. RNA polymerase is physically blocked by the promoter sequence.
C. cAMP levels decrease, preventing the activation of the CAP protein.
D. Allolactose binds to the repressor, causing it to release from the operator, allowing high
levels of transcription.
Correct Answer: D
,Explanation: When lactose is present, it is converted to allolactose which acts as an
inducer by binding to the lac repressor. This binding causes a conformational change that
prevents the repressor from sticking to the operator site. Since glucose is absent, cAMP
levels are high, activating CAP and ensuring robust transcription of the structural genes.
4. Which type of mutation results in the replacement of a single nucleotide, leading to a
change in one amino acid in the resulting protein?
A. Silent mutation
B. Nonsense mutation
C. Missense mutation
D. Frameshift mutation
Correct Answer: C
Explanation: A missense mutation is a type of point mutation where a change in a single
base pair results in a different amino acid being incorporated into the polypeptide chain.
This can have varying effects on protein function depending on the chemical properties of
the new amino acid. In contrast, silent mutations do not change the amino acid, and
nonsense mutations create premature stop codons.
5. What is the primary function of the enzyme DNA Ligase during the process of DNA
replication?
A. To unwind the double helix at the replication fork.
B. To remove RNA primers and replace them with DNA.
, C. To proofread the newly synthesized DNA for errors.
D. To join Okazaki fragments together on the lagging strand by forming phosphodiester
bonds.
Correct Answer: D
Explanation: DNA Ligase is essential for sealing nicks in the sugar-phosphate backbone of
DNA. Specifically, it connects Okazaki fragments on the lagging strand after DNA
polymerase I has replaced the RNA primers with DNA nucleotides. This action results in a
continuous, unbroken strand of DNA.
6. The process of transcription begins when RNA polymerase binds to a specific DNA
sequence known as the:
A. Origin of replication
B. Promoter
C. Stop codon
D. Anticodon
Correct Answer: B
Explanation: The promoter is a specific regulatory sequence located upstream of a gene
that signals the start of transcription. RNA polymerase recognizes and binds to this site to
initiate the synthesis of an RNA molecule. The promoter determines which DNA strand will
serve as the template and establishes the transcription start site.
Q&A with Rationale (BIO250 Exam 3) |
StraighterLine
1. Which enzyme is responsible for synthesizing a short RNA primer to provide a 3’-OH group
for DNA polymerase III to begin DNA synthesis?
A. DNA Ligase
B. Gyrase
C. Helicase
D. Primase
Correct Answer: D
Explanation: Primase is a specialized RNA polymerase that synthesizes a short RNA
primer required for DNA replication. DNA polymerase III cannot initiate synthesis on a
bare template and requires the free 3’-OH group provided by this primer. Once the primer
is in place, DNA polymerase III can extend the new DNA strand in the 5’ to 3’ direction.
2. Select all that apply: Which of the following are recognized mechanisms of horizontal gene
transfer (HGT) in prokaryotic organisms?
A. Conjugation
B. Transformation
C. Binary Fission
,D. Transduction
E. Transposition via transposons
F. Mitotic Division
Correct Answer: A, B, D, E
Explanation: Horizontal gene transfer involves the movement of genetic material between
non-parental cells through processes like conjugation, transformation, and transduction.
Conjugation requires direct cell-to-cell contact, transformation involves the uptake of
naked DNA, and transduction is mediated by bacteriophages. Transposition involves
jumping genes that can move between the chromosome and plasmids, whereas binary
fission and mitosis are forms of vertical transmission.
3. In the context of the lac operon, what occurs when lactose is present in the environment
but glucose is absent?
A. The repressor remains bound to the operator, preventing transcription.
B. RNA polymerase is physically blocked by the promoter sequence.
C. cAMP levels decrease, preventing the activation of the CAP protein.
D. Allolactose binds to the repressor, causing it to release from the operator, allowing high
levels of transcription.
Correct Answer: D
,Explanation: When lactose is present, it is converted to allolactose which acts as an
inducer by binding to the lac repressor. This binding causes a conformational change that
prevents the repressor from sticking to the operator site. Since glucose is absent, cAMP
levels are high, activating CAP and ensuring robust transcription of the structural genes.
4. Which type of mutation results in the replacement of a single nucleotide, leading to a
change in one amino acid in the resulting protein?
A. Silent mutation
B. Nonsense mutation
C. Missense mutation
D. Frameshift mutation
Correct Answer: C
Explanation: A missense mutation is a type of point mutation where a change in a single
base pair results in a different amino acid being incorporated into the polypeptide chain.
This can have varying effects on protein function depending on the chemical properties of
the new amino acid. In contrast, silent mutations do not change the amino acid, and
nonsense mutations create premature stop codons.
5. What is the primary function of the enzyme DNA Ligase during the process of DNA
replication?
A. To unwind the double helix at the replication fork.
B. To remove RNA primers and replace them with DNA.
, C. To proofread the newly synthesized DNA for errors.
D. To join Okazaki fragments together on the lagging strand by forming phosphodiester
bonds.
Correct Answer: D
Explanation: DNA Ligase is essential for sealing nicks in the sugar-phosphate backbone of
DNA. Specifically, it connects Okazaki fragments on the lagging strand after DNA
polymerase I has replaced the RNA primers with DNA nucleotides. This action results in a
continuous, unbroken strand of DNA.
6. The process of transcription begins when RNA polymerase binds to a specific DNA
sequence known as the:
A. Origin of replication
B. Promoter
C. Stop codon
D. Anticodon
Correct Answer: B
Explanation: The promoter is a specific regulatory sequence located upstream of a gene
that signals the start of transcription. RNA polymerase recognizes and binds to this site to
initiate the synthesis of an RNA molecule. The promoter determines which DNA strand will
serve as the template and establishes the transcription start site.
