NR 507 Advanced Pathophysiology Midterm
Exam Official Practice Exam Actual Exam
2026/2027 with Detailed Rationales | Complete
Exam-Style Questions | Pass Guaranteed – A+
Graded
══════════════════════════════════════
SECTION 1: CELLULAR BIOLOGY & GENETICS Q1 – Q10
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Question 1 of 50
A 34-year-old woman presents with progressive muscle weakness and episodes of
rhabdomyolysis after moderate exercise. Muscle biopsy reveals subsarcolemmal
accumulations of abnormal mitochondria. Genetic testing identifies a mutation in the gene
encoding mitochondrial DNA polymerase gamma. Her physician explains that this mutation
most directly impairs which cellular process?
A. Glycolytic ATP generation in the cytosol
B. Oxidative phosphorylation within the mitochondrial matrix
C. Protein synthesis on cytosolic ribosomes
D. Cholesterol synthesis in the smooth endoplasmic reticulum
Correct Answer: B
Rationale: Mitochondrial DNA polymerase gamma is the sole polymerase responsible for
replicating and repairing mitochondrial DNA, which encodes critical subunits of the electron
transport chain and ATP synthase; impaired mtDNA maintenance directly cripples oxidative
phosphorylation. Glycolytic ATP generation occurs in the cytosol and is nuclear-encoded, so
it remains unaffected by this specific mitochondrial polymerase defect. Clinically,
mitochondrial myopathies classically present with exercise intolerance because oxidative
phosphorylation cannot meet increased ATP demands.
Question 2 of 50
A 7-year-old boy is evaluated for developmental delay, ataxia, and cherry-red spots on macular
examination. Enzyme assay reveals absent hexosaminidase A activity. The pathophysiologic
mechanism responsible for his neurologic deterioration involves accumulation of which
substrate within neuronal lysosomes?
,A. Glucocerebroside
B. GM2 ganglioside
C. Sphingomyelin
D. Globotriaosylceramide
Correct Answer: B
Rationale: Hexosaminidase A deficiency defines Tay-Sachs disease, wherein the enzyme
cannot cleave N-acetylgalactosamine from GM2 ganglioside, leading to indigestible substrate
accumulation in neuronal lysosomes and subsequent neurodegeneration. Glucocerebroside
accumulates in Gaucher disease due to beta-glucocerebrosidase deficiency, while
sphingomyelin accumulation characterizes Niemann-Pick disease. The cherry-red spot is a
classic but nonspecific funduscopic finding in GM2 gangliosidosis caused by ganglioside
storage in retinal ganglion cells.
Question 3 of 50
A 52-year-old man with a 40 pack-year smoking history develops a persistent cough and
hemoptysis. CT-guided biopsy of a hilar mass reveals small cell carcinoma. Molecular
analysis shows inactivation of both RB1 alleles. This tumor suppressor gene normally
regulates cell cycle progression by exerting its effect at which specific checkpoint?
A. The G1/S transition through sequestration of E2F transcription factors
B. The G2/M transition through inhibition of cyclin B-CDK1 complexes
C. The metaphase-anaphase transition through regulation of cohesin complexes
D. The restriction point through activation of p53-mediated transcription
Correct Answer: A
Rationale: The retinoblastoma protein (pRb) binds and inhibits E2F family transcription
factors during G1, preventing S-phase entry; loss of RB1 function releases E2F to drive
uncontrolled DNA replication and cell cycle progression. The G2/M checkpoint is primarily
governed by p53 and the DNA damage response, not RB1, while cohesin regulation occurs
independently during mitosis. Small cell lung carcinoma is among the malignancies most
characteristically associated with biallelic RB1 inactivation, making this a high-yield
pathophysiology correlation.
Question 4 of 50
A 28-year-old woman of Ashkenazi Jewish descent presents with recurrent pulmonary
infections and steatorrhea. Sweat chloride testing reveals a value of 82 mEq/L. Genetic
analysis identifies a deletion of phenylalanine at position 508 in the CFTR protein. This
mutation impairs chloride transport primarily by causing which defect in protein processing?
A. Defective glycosylation at the Golgi apparatus
B. Misfolding and premature degradation by endoplasmic reticulum-associated degradation
, C. Failure of signal peptide cleavage during translation
D. Aberrant targeting to the lysosomal compartment instead of the plasma membrane
Correct Answer: B
Rationale: The ΔF508 mutation introduces a conformational defect in the CFTR protein that
prevents proper folding in the endoplasmic reticulum, triggering recognition by
chaperone-mediated quality control and subsequent proteasomal degradation before the
protein reaches the plasma membrane. Glycosylation defects and signal peptide cleavage
failures are not the primary mechanisms of ΔF508 pathophysiology, and lysosomal
misrouting is characteristic of I-cell disease, not cystic fibrosis. The resulting absence of
functional CFTR at the apical membrane abolishes cAMP-regulated chloride secretion and
disrupts mucociliary clearance.
Question 5 of 50
A 45-year-old man with chronic alcohol use disorder presents with numbness in his feet and
gait instability. Serum thiamine levels are undetectable. His neurologic deficits are most
directly attributable to impaired function of which enzyme-dependent process in glucose
metabolism?
A. Pyruvate dehydrogenase complex converting pyruvate to acetyl-CoA
B. Lactate dehydrogenase converting pyruvate to lactate
C. Glucose-6-phosphatase converting glucose-6-phosphate to glucose
D. Phosphofructokinase-1 converting fructose-6-phosphate to fructose-1,6-bisphosphate
Correct Answer: A
Rationale: Thiamine pyrophosphate is an essential cofactor for pyruvate dehydrogenase,
alpha-ketoglutarate dehydrogenase, and transketolase; deficiency impairs aerobic glucose
metabolism and causes lactic acidosis while depriving the nervous system of ATP and
acetylcholine precursors. Lactate dehydrogenase does not require thiamine, and
glucose-6-phosphatase and phosphofructokinase-1 operate independently of this cofactor.
The peripheral neuropathy and ataxia in Wernicke-Korsakoff syndrome reflect the high
metabolic demand and thiamine dependence of neuronal tissue.
Question 6 of 50
A 16-year-old male athlete collapses during a basketball game and is found to have
hypertrophic cardiomyopathy on autopsy. Genetic testing reveals a missense mutation in the
MYH7 gene encoding beta-myosin heavy chain. This mutation produces its pathologic effect
primarily through which mechanism?
A. Gain-of-function leading to hypercontractility and sarcomere disarray
B. Dominant-negative interference with normal sarcomere assembly
C. Loss-of-function causing dilated cardiomyopathy through haploinsufficiency
Exam Official Practice Exam Actual Exam
2026/2027 with Detailed Rationales | Complete
Exam-Style Questions | Pass Guaranteed – A+
Graded
══════════════════════════════════════
SECTION 1: CELLULAR BIOLOGY & GENETICS Q1 – Q10
══════════════════════════════════════
Question 1 of 50
A 34-year-old woman presents with progressive muscle weakness and episodes of
rhabdomyolysis after moderate exercise. Muscle biopsy reveals subsarcolemmal
accumulations of abnormal mitochondria. Genetic testing identifies a mutation in the gene
encoding mitochondrial DNA polymerase gamma. Her physician explains that this mutation
most directly impairs which cellular process?
A. Glycolytic ATP generation in the cytosol
B. Oxidative phosphorylation within the mitochondrial matrix
C. Protein synthesis on cytosolic ribosomes
D. Cholesterol synthesis in the smooth endoplasmic reticulum
Correct Answer: B
Rationale: Mitochondrial DNA polymerase gamma is the sole polymerase responsible for
replicating and repairing mitochondrial DNA, which encodes critical subunits of the electron
transport chain and ATP synthase; impaired mtDNA maintenance directly cripples oxidative
phosphorylation. Glycolytic ATP generation occurs in the cytosol and is nuclear-encoded, so
it remains unaffected by this specific mitochondrial polymerase defect. Clinically,
mitochondrial myopathies classically present with exercise intolerance because oxidative
phosphorylation cannot meet increased ATP demands.
Question 2 of 50
A 7-year-old boy is evaluated for developmental delay, ataxia, and cherry-red spots on macular
examination. Enzyme assay reveals absent hexosaminidase A activity. The pathophysiologic
mechanism responsible for his neurologic deterioration involves accumulation of which
substrate within neuronal lysosomes?
,A. Glucocerebroside
B. GM2 ganglioside
C. Sphingomyelin
D. Globotriaosylceramide
Correct Answer: B
Rationale: Hexosaminidase A deficiency defines Tay-Sachs disease, wherein the enzyme
cannot cleave N-acetylgalactosamine from GM2 ganglioside, leading to indigestible substrate
accumulation in neuronal lysosomes and subsequent neurodegeneration. Glucocerebroside
accumulates in Gaucher disease due to beta-glucocerebrosidase deficiency, while
sphingomyelin accumulation characterizes Niemann-Pick disease. The cherry-red spot is a
classic but nonspecific funduscopic finding in GM2 gangliosidosis caused by ganglioside
storage in retinal ganglion cells.
Question 3 of 50
A 52-year-old man with a 40 pack-year smoking history develops a persistent cough and
hemoptysis. CT-guided biopsy of a hilar mass reveals small cell carcinoma. Molecular
analysis shows inactivation of both RB1 alleles. This tumor suppressor gene normally
regulates cell cycle progression by exerting its effect at which specific checkpoint?
A. The G1/S transition through sequestration of E2F transcription factors
B. The G2/M transition through inhibition of cyclin B-CDK1 complexes
C. The metaphase-anaphase transition through regulation of cohesin complexes
D. The restriction point through activation of p53-mediated transcription
Correct Answer: A
Rationale: The retinoblastoma protein (pRb) binds and inhibits E2F family transcription
factors during G1, preventing S-phase entry; loss of RB1 function releases E2F to drive
uncontrolled DNA replication and cell cycle progression. The G2/M checkpoint is primarily
governed by p53 and the DNA damage response, not RB1, while cohesin regulation occurs
independently during mitosis. Small cell lung carcinoma is among the malignancies most
characteristically associated with biallelic RB1 inactivation, making this a high-yield
pathophysiology correlation.
Question 4 of 50
A 28-year-old woman of Ashkenazi Jewish descent presents with recurrent pulmonary
infections and steatorrhea. Sweat chloride testing reveals a value of 82 mEq/L. Genetic
analysis identifies a deletion of phenylalanine at position 508 in the CFTR protein. This
mutation impairs chloride transport primarily by causing which defect in protein processing?
A. Defective glycosylation at the Golgi apparatus
B. Misfolding and premature degradation by endoplasmic reticulum-associated degradation
, C. Failure of signal peptide cleavage during translation
D. Aberrant targeting to the lysosomal compartment instead of the plasma membrane
Correct Answer: B
Rationale: The ΔF508 mutation introduces a conformational defect in the CFTR protein that
prevents proper folding in the endoplasmic reticulum, triggering recognition by
chaperone-mediated quality control and subsequent proteasomal degradation before the
protein reaches the plasma membrane. Glycosylation defects and signal peptide cleavage
failures are not the primary mechanisms of ΔF508 pathophysiology, and lysosomal
misrouting is characteristic of I-cell disease, not cystic fibrosis. The resulting absence of
functional CFTR at the apical membrane abolishes cAMP-regulated chloride secretion and
disrupts mucociliary clearance.
Question 5 of 50
A 45-year-old man with chronic alcohol use disorder presents with numbness in his feet and
gait instability. Serum thiamine levels are undetectable. His neurologic deficits are most
directly attributable to impaired function of which enzyme-dependent process in glucose
metabolism?
A. Pyruvate dehydrogenase complex converting pyruvate to acetyl-CoA
B. Lactate dehydrogenase converting pyruvate to lactate
C. Glucose-6-phosphatase converting glucose-6-phosphate to glucose
D. Phosphofructokinase-1 converting fructose-6-phosphate to fructose-1,6-bisphosphate
Correct Answer: A
Rationale: Thiamine pyrophosphate is an essential cofactor for pyruvate dehydrogenase,
alpha-ketoglutarate dehydrogenase, and transketolase; deficiency impairs aerobic glucose
metabolism and causes lactic acidosis while depriving the nervous system of ATP and
acetylcholine precursors. Lactate dehydrogenase does not require thiamine, and
glucose-6-phosphatase and phosphofructokinase-1 operate independently of this cofactor.
The peripheral neuropathy and ataxia in Wernicke-Korsakoff syndrome reflect the high
metabolic demand and thiamine dependence of neuronal tissue.
Question 6 of 50
A 16-year-old male athlete collapses during a basketball game and is found to have
hypertrophic cardiomyopathy on autopsy. Genetic testing reveals a missense mutation in the
MYH7 gene encoding beta-myosin heavy chain. This mutation produces its pathologic effect
primarily through which mechanism?
A. Gain-of-function leading to hypercontractility and sarcomere disarray
B. Dominant-negative interference with normal sarcomere assembly
C. Loss-of-function causing dilated cardiomyopathy through haploinsufficiency
