, Question 1
A researcher treats isolated mitochondria with oligomycin and then measures
oxygen consumption and ATP synthesis. Which of the following best explains
the observed decrease in oxygen consumption?
A. Oligomycin directly inhibits Complex IV, preventing electron transfer
to oxygen.
B. Oligomycin blocks ATP synthase proton flow, causing proton gradient
buildup that thermodynamically back-pressures the electron transport
chain.
C. Oligomycin uncouples the proton gradient by transporting protons
across the inner membrane.
D. Oligomycin inhibits the malate-aspartate shuttle, reducing NADH
delivery to the matrix.
Correct Answer: B - Oligomycin blocks ATP synthase proton
flow, causing proton gradient buildup that thermodynamically
back-pressures the electron transport chain.
RATIONALE
Oligomycin inhibits the Fo subunit of ATP synthase, blocking proton
translocation and causing the proton motive force to rise; this
back-pressure slows electron transport and thus oxygen consumption.
It does not inhibit Complex IV, uncouple, or affect shuttle activity.
Question 2
In a eukaryotic mRNA, a silent mutation occurs within an exonic splicing
enhancer (ESE) sequence. Which of the following is the most likely
consequence?
A. No effect on protein sequence because silent mutations do not alter
amino acids.
B. Exon skipping or alternative splicing leading to a truncated or aberrant
protein.
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, C. Frameshift mutation downstream of the ESE.
D. Premature termination of transcription by RNA polymerase II.
Correct Answer: B - Exon skipping or alternative splicing leading
to a truncated or aberrant protein.
RATIONALE
Silent mutations can disrupt ESEs, altering splicing and causing exon
skipping or aberrant isoforms, which may produce nonfunctional
proteins. They do not cause frameshifts or affect transcription
termination.
Question 3
A population of birds on an island has a mean beak depth of 10 mm. After a
drought, only birds with beak depths >12 mm survive. The next generation's
mean beak depth is 12.5 mm. What is the selection differential (S) and
response to selection (R)?
A. S = 2 mm; R = 0.5 mm
B. S = 0.5 mm; R = 2 mm
C. S = 2.5 mm; R = 2 mm
D. S = 10 mm; R = 12.5 mm
Correct Answer: A - S = 2 mm; R = 0.5 mm
RATIONALE
Selection differential S is the difference between the mean of selected
parents (12 mm) and the overall population mean (10 mm), so S = 2
mm. Response R is the difference between offspring mean (12.5 mm)
and original population mean (10 mm), so R = 0.5 mm.
Question 4
Which of the following best explains why the oxygen dissociation curve of
fetal hemoglobin (HbF) is left-shifted relative to maternal hemoglobin (HbA)?
A. HbF has a higher affinity for 2,3-BPG than HbA.
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, B. HbF binds 2,3-BPG less effectively due to its gamma chains,
increasing oxygen affinity.
C. HbF has a lower affinity for oxygen, facilitating oxygen transfer to
maternal blood.
D. HbF exhibits a Bohr effect that is more pronounced than that of HbA.
Correct Answer: B - HbF binds 2,3-BPG less effectively due to its
gamma chains, increasing oxygen affinity.
RATIONALE
HbF has gamma chains that interact poorly with 2,3-BPG, reducing its
stabilizing effect on the T state and increasing oxygen affinity, which
facilitates oxygen transfer from mother to fetus. The other options
misstate the mechanism or direction of the shift.
Question 5
During a laboratory experiment, a cell is treated with a drug that inhibits the
Na+/K+ ATPase. Which of the following immediate consequences is most
likely?
A. Increased intracellular Na+ and decreased intracellular K+
B. Decreased intracellular Na+ and increased intracellular K+
C. Hyperpolarization of the cell membrane
D. Increased secondary active transport of glucose
Correct Answer: A - Increased intracellular Na+ and decreased
intracellular K+
RATIONALE
Inhibition of Na+/K+ ATPase prevents extrusion of Na+ and uptake of
K+, leading to intracellular Na+ accumulation and K+ depletion, and
depolarization. Secondary active transport that depends on the Na+
gradient would be impaired, not increased.
Page 4
A researcher treats isolated mitochondria with oligomycin and then measures
oxygen consumption and ATP synthesis. Which of the following best explains
the observed decrease in oxygen consumption?
A. Oligomycin directly inhibits Complex IV, preventing electron transfer
to oxygen.
B. Oligomycin blocks ATP synthase proton flow, causing proton gradient
buildup that thermodynamically back-pressures the electron transport
chain.
C. Oligomycin uncouples the proton gradient by transporting protons
across the inner membrane.
D. Oligomycin inhibits the malate-aspartate shuttle, reducing NADH
delivery to the matrix.
Correct Answer: B - Oligomycin blocks ATP synthase proton
flow, causing proton gradient buildup that thermodynamically
back-pressures the electron transport chain.
RATIONALE
Oligomycin inhibits the Fo subunit of ATP synthase, blocking proton
translocation and causing the proton motive force to rise; this
back-pressure slows electron transport and thus oxygen consumption.
It does not inhibit Complex IV, uncouple, or affect shuttle activity.
Question 2
In a eukaryotic mRNA, a silent mutation occurs within an exonic splicing
enhancer (ESE) sequence. Which of the following is the most likely
consequence?
A. No effect on protein sequence because silent mutations do not alter
amino acids.
B. Exon skipping or alternative splicing leading to a truncated or aberrant
protein.
Page 2
, C. Frameshift mutation downstream of the ESE.
D. Premature termination of transcription by RNA polymerase II.
Correct Answer: B - Exon skipping or alternative splicing leading
to a truncated or aberrant protein.
RATIONALE
Silent mutations can disrupt ESEs, altering splicing and causing exon
skipping or aberrant isoforms, which may produce nonfunctional
proteins. They do not cause frameshifts or affect transcription
termination.
Question 3
A population of birds on an island has a mean beak depth of 10 mm. After a
drought, only birds with beak depths >12 mm survive. The next generation's
mean beak depth is 12.5 mm. What is the selection differential (S) and
response to selection (R)?
A. S = 2 mm; R = 0.5 mm
B. S = 0.5 mm; R = 2 mm
C. S = 2.5 mm; R = 2 mm
D. S = 10 mm; R = 12.5 mm
Correct Answer: A - S = 2 mm; R = 0.5 mm
RATIONALE
Selection differential S is the difference between the mean of selected
parents (12 mm) and the overall population mean (10 mm), so S = 2
mm. Response R is the difference between offspring mean (12.5 mm)
and original population mean (10 mm), so R = 0.5 mm.
Question 4
Which of the following best explains why the oxygen dissociation curve of
fetal hemoglobin (HbF) is left-shifted relative to maternal hemoglobin (HbA)?
A. HbF has a higher affinity for 2,3-BPG than HbA.
Page 3
, B. HbF binds 2,3-BPG less effectively due to its gamma chains,
increasing oxygen affinity.
C. HbF has a lower affinity for oxygen, facilitating oxygen transfer to
maternal blood.
D. HbF exhibits a Bohr effect that is more pronounced than that of HbA.
Correct Answer: B - HbF binds 2,3-BPG less effectively due to its
gamma chains, increasing oxygen affinity.
RATIONALE
HbF has gamma chains that interact poorly with 2,3-BPG, reducing its
stabilizing effect on the T state and increasing oxygen affinity, which
facilitates oxygen transfer from mother to fetus. The other options
misstate the mechanism or direction of the shift.
Question 5
During a laboratory experiment, a cell is treated with a drug that inhibits the
Na+/K+ ATPase. Which of the following immediate consequences is most
likely?
A. Increased intracellular Na+ and decreased intracellular K+
B. Decreased intracellular Na+ and increased intracellular K+
C. Hyperpolarization of the cell membrane
D. Increased secondary active transport of glucose
Correct Answer: A - Increased intracellular Na+ and decreased
intracellular K+
RATIONALE
Inhibition of Na+/K+ ATPase prevents extrusion of Na+ and uptake of
K+, leading to intracellular Na+ accumulation and K+ depletion, and
depolarization. Secondary active transport that depends on the Na+
gradient would be impaired, not increased.
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