BIO 250 Exam 3 V1 | BIO 250 Microbiology | Actual
Q&A with Rationale (BIO250 Exam 3) |
StraighterLine
1. During DNA replication, which of the following enzymes are directly involved in the
synthesis and maintenance of the new DNA strands? (Select All That Apply)
A. Helicase
B. DNA Polymerase III
C. Spliceosome
D. DNA Ligase
E. Primase
F. Reverse Transcriptase
Correct Answer: A, B, D, E
Explanation: DNA replication requires a suite of specialized enzymes to ensure accuracy
and speed. Helicase unwinds the double helix, while Primase provides the necessary RNA
primers for DNA Polymerase III to begin elongation. DNA Ligase eventually joins the
Okazaki fragments on the lagging strand to create a continuous DNA molecule.
2. Which of the following best describes the function of a ‘promoter’ region in bacterial
genetics?
A. The site where translation is terminated.
,B. The location where DNA replication begins.
C. A protein that represses gene expression.
D. The specific DNA sequence where RNA polymerase binds to initiate transcription.
Correct Answer: D
Explanation: The promoter is a crucial regulatory element located upstream of the
structural genes in an operon. It serves as the recognition site for RNA polymerase,
facilitating the correct positioning of the enzyme to start mRNA synthesis. Without a
functional promoter, the gene cannot be transcribed into mRNA.
3. In the context of the lac operon, what occurs when lactose is present and glucose is absent
in the environment?
A. The repressor remains bound to the operator, preventing transcription.
B. Allolactose binds to the repressor, inactivating it and allowing transcription to proceed.
C. The CAP protein is inactive, leading to low transcription levels.
D. Transcription is inhibited by high levels of cAMP.
Correct Answer: B
Explanation: The lac operon is an inducible system designed to utilize lactose only when
necessary. Allolactose acts as an inducer by binding to the repressor protein, causing a
conformational change that releases it from the operator. This allows RNA polymerase to
transcribe the genes required for lactose metabolism.
, 4. Which type of mutation results in a premature stop codon and typically leads to a
nonfunctional protein?
A. Nonsense mutation
B. Missense mutation
C. Silent mutation
D. Reverse mutation
Correct Answer: A
Explanation: A nonsense mutation occurs when a single nucleotide substitution changes a
codon that specifies an amino acid into a stop codon. This leads to the truncation of the
polypeptide chain during translation. Because the resulting protein is missing essential
domains, it is almost always biologically inactive.
5. Which horizontal gene transfer mechanism requires direct cell-to-cell contact between a
donor and a recipient?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: C
Q&A with Rationale (BIO250 Exam 3) |
StraighterLine
1. During DNA replication, which of the following enzymes are directly involved in the
synthesis and maintenance of the new DNA strands? (Select All That Apply)
A. Helicase
B. DNA Polymerase III
C. Spliceosome
D. DNA Ligase
E. Primase
F. Reverse Transcriptase
Correct Answer: A, B, D, E
Explanation: DNA replication requires a suite of specialized enzymes to ensure accuracy
and speed. Helicase unwinds the double helix, while Primase provides the necessary RNA
primers for DNA Polymerase III to begin elongation. DNA Ligase eventually joins the
Okazaki fragments on the lagging strand to create a continuous DNA molecule.
2. Which of the following best describes the function of a ‘promoter’ region in bacterial
genetics?
A. The site where translation is terminated.
,B. The location where DNA replication begins.
C. A protein that represses gene expression.
D. The specific DNA sequence where RNA polymerase binds to initiate transcription.
Correct Answer: D
Explanation: The promoter is a crucial regulatory element located upstream of the
structural genes in an operon. It serves as the recognition site for RNA polymerase,
facilitating the correct positioning of the enzyme to start mRNA synthesis. Without a
functional promoter, the gene cannot be transcribed into mRNA.
3. In the context of the lac operon, what occurs when lactose is present and glucose is absent
in the environment?
A. The repressor remains bound to the operator, preventing transcription.
B. Allolactose binds to the repressor, inactivating it and allowing transcription to proceed.
C. The CAP protein is inactive, leading to low transcription levels.
D. Transcription is inhibited by high levels of cAMP.
Correct Answer: B
Explanation: The lac operon is an inducible system designed to utilize lactose only when
necessary. Allolactose acts as an inducer by binding to the repressor protein, causing a
conformational change that releases it from the operator. This allows RNA polymerase to
transcribe the genes required for lactose metabolism.
, 4. Which type of mutation results in a premature stop codon and typically leads to a
nonfunctional protein?
A. Nonsense mutation
B. Missense mutation
C. Silent mutation
D. Reverse mutation
Correct Answer: A
Explanation: A nonsense mutation occurs when a single nucleotide substitution changes a
codon that specifies an amino acid into a stop codon. This leads to the truncation of the
polypeptide chain during translation. Because the resulting protein is missing essential
domains, it is almost always biologically inactive.
5. Which horizontal gene transfer mechanism requires direct cell-to-cell contact between a
donor and a recipient?
A. Transformation
B. Transduction
C. Conjugation
D. Transposition
Correct Answer: C
