, Question 1
A cell exposed to prolonged sublethal hypoxia accumulates misfolded proteins
in the endoplasmic reticulum. Which downstream event most directly commits
this cell to irreversible injury?
A. Activation of the unfolded protein response with chaperone
upregulation
B. Mitochondrial permeability transition pore opening with cytochrome c
release
C. Autophagic sequestration of damaged organelles
D. Upregulation of heat shock proteins and antioxidant enzymes
Correct Answer: B - Mitochondrial permeability transition pore
opening with cytochrome c release
RATIONALE
The mitochondrial permeability transition pore opening dissipates the
proton gradient, halts ATP synthesis, and releases cytochrome c,
committing the cell to necrosis or apoptosis. UPR activation,
autophagy, and heat shock responses are adaptive attempts to restore
homeostasis and are potentially reversible. Thus, only MPT opening
marks the point of no return.
Question 2
In a tumor, a mutation in the promoter region of a DNA mismatch repair gene
leads to hypermethylation and transcriptional silencing. This best exemplifies
which mechanism?
A. Loss of heterozygosity
B. Chromosomal translocation
C. Epigenetic silencing of a tumor suppressor
D. Gain-of-function oncogene activation
Correct Answer: C - Epigenetic silencing of a tumor suppressor
Page 2
, RATIONALE
Hypermethylation of a promoter CpG island silences gene expression
without altering the DNA sequence, which is epigenetic silencing.
Mismatch repair genes are tumor suppressors, so silencing them
promotes microsatellite instability. Loss of heterozygosity,
translocation, and oncogene activation involve structural or sequence
changes, not epigenetic regulation.
Question 3
Which immunoglobulin is most efficient at activating the classical complement
pathway, and what structural feature explains this?
A. IgA; secretory component enhances C1q binding
B. IgE; high-affinity FcRI cross-linking
C. IgG3; multiple Fc regions in close proximity after antigen binding
D. IgM; pentameric structure allows simultaneous binding of multiple
C1q heads
Correct Answer: D - IgM; pentameric structure allows
simultaneous binding of multiple C1q heads
RATIONALE
IgM's pentameric structure permits simultaneous binding of multiple
C1q globular heads to a single antigen-bound molecule, dramatically
increasing complement activation efficiency. IgG3 can activate
complement but requires multiple IgG molecules bound in close
proximity. IgA and IgE do not efficiently activate the classical
pathway.
Question 4
A patient with chronic kidney disease has an eGFR of 25 mL/min/1.73 m².
Which laboratory finding is most consistent with secondary
hyperparathyroidism in this context?
A. Elevated serum phosphate and low serum calcium
Page 3
, B. Low serum phosphate and elevated serum calcium
C. Elevated serum phosphate and elevated serum calcium
D. Low serum phosphate and low serum calcium
Correct Answer: A - Elevated serum phosphate and low serum
calcium
RATIONALE
In CKD, reduced phosphate excretion leads to hyperphosphatemia,
which complexes with calcium and lowers ionized calcium. The
resulting hypocalcemia and hyperphosphatemia stimulate PTH
secretion, causing secondary hyperparathyroidism. Elevated calcium
would suppress PTH, and low phosphate is not typical of advanced
CKD.
Question 5
Which statement best distinguishes the pathophysiology of type 1 from type 2
diabetes mellitus regarding insulin secretion?
A. Type 1 involves insulin resistance with compensatory
hyperinsulinemia; type 2 involves absolute insulin deficiency.
B. Type 1 involves autoimmune beta-cell destruction with absolute
insulin deficiency; type 2 involves progressive beta-cell dysfunction with
relative insulin deficiency.
C. Both types involve absolute insulin deficiency from birth.
D. Type 1 is characterized by normal insulin secretion but receptor
defects; type 2 by autoimmune destruction.
Correct Answer: B - Type 1 involves autoimmune beta-cell
destruction with absolute insulin deficiency; type 2 involves
progressive beta-cell dysfunction with relative insulin deficiency.
Page 4
A cell exposed to prolonged sublethal hypoxia accumulates misfolded proteins
in the endoplasmic reticulum. Which downstream event most directly commits
this cell to irreversible injury?
A. Activation of the unfolded protein response with chaperone
upregulation
B. Mitochondrial permeability transition pore opening with cytochrome c
release
C. Autophagic sequestration of damaged organelles
D. Upregulation of heat shock proteins and antioxidant enzymes
Correct Answer: B - Mitochondrial permeability transition pore
opening with cytochrome c release
RATIONALE
The mitochondrial permeability transition pore opening dissipates the
proton gradient, halts ATP synthesis, and releases cytochrome c,
committing the cell to necrosis or apoptosis. UPR activation,
autophagy, and heat shock responses are adaptive attempts to restore
homeostasis and are potentially reversible. Thus, only MPT opening
marks the point of no return.
Question 2
In a tumor, a mutation in the promoter region of a DNA mismatch repair gene
leads to hypermethylation and transcriptional silencing. This best exemplifies
which mechanism?
A. Loss of heterozygosity
B. Chromosomal translocation
C. Epigenetic silencing of a tumor suppressor
D. Gain-of-function oncogene activation
Correct Answer: C - Epigenetic silencing of a tumor suppressor
Page 2
, RATIONALE
Hypermethylation of a promoter CpG island silences gene expression
without altering the DNA sequence, which is epigenetic silencing.
Mismatch repair genes are tumor suppressors, so silencing them
promotes microsatellite instability. Loss of heterozygosity,
translocation, and oncogene activation involve structural or sequence
changes, not epigenetic regulation.
Question 3
Which immunoglobulin is most efficient at activating the classical complement
pathway, and what structural feature explains this?
A. IgA; secretory component enhances C1q binding
B. IgE; high-affinity FcRI cross-linking
C. IgG3; multiple Fc regions in close proximity after antigen binding
D. IgM; pentameric structure allows simultaneous binding of multiple
C1q heads
Correct Answer: D - IgM; pentameric structure allows
simultaneous binding of multiple C1q heads
RATIONALE
IgM's pentameric structure permits simultaneous binding of multiple
C1q globular heads to a single antigen-bound molecule, dramatically
increasing complement activation efficiency. IgG3 can activate
complement but requires multiple IgG molecules bound in close
proximity. IgA and IgE do not efficiently activate the classical
pathway.
Question 4
A patient with chronic kidney disease has an eGFR of 25 mL/min/1.73 m².
Which laboratory finding is most consistent with secondary
hyperparathyroidism in this context?
A. Elevated serum phosphate and low serum calcium
Page 3
, B. Low serum phosphate and elevated serum calcium
C. Elevated serum phosphate and elevated serum calcium
D. Low serum phosphate and low serum calcium
Correct Answer: A - Elevated serum phosphate and low serum
calcium
RATIONALE
In CKD, reduced phosphate excretion leads to hyperphosphatemia,
which complexes with calcium and lowers ionized calcium. The
resulting hypocalcemia and hyperphosphatemia stimulate PTH
secretion, causing secondary hyperparathyroidism. Elevated calcium
would suppress PTH, and low phosphate is not typical of advanced
CKD.
Question 5
Which statement best distinguishes the pathophysiology of type 1 from type 2
diabetes mellitus regarding insulin secretion?
A. Type 1 involves insulin resistance with compensatory
hyperinsulinemia; type 2 involves absolute insulin deficiency.
B. Type 1 involves autoimmune beta-cell destruction with absolute
insulin deficiency; type 2 involves progressive beta-cell dysfunction with
relative insulin deficiency.
C. Both types involve absolute insulin deficiency from birth.
D. Type 1 is characterized by normal insulin secretion but receptor
defects; type 2 by autoimmune destruction.
Correct Answer: B - Type 1 involves autoimmune beta-cell
destruction with absolute insulin deficiency; type 2 involves
progressive beta-cell dysfunction with relative insulin deficiency.
Page 4
