COMSAE PHASE 1 FORM 115 EXAMINATION
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Question 1
A 24-year-old woman has a mutation that prevents the β subunit of a
heterotrimeric G protein from exchanging GDP for GTP. Which cellular
process is most directly impaired?
A. Activation of adenylyl cyclase
B. Phosphorylation of receptor tyrosine kinases
C. Opening of voltage-gated sodium channels
D. Synthesis of phosphatidylcholine
E. Degradation of cyclic AMP
Answer: A. Activation of adenylyl cyclase
Rationale: G-protein-coupled receptors activate heterotrimeric G
proteins by promoting GDP-GTP exchange, allowing the Gα subunit to
regulate adenylyl cyclase and other effectors.
Question 2
A patient with severe diarrhea develops metabolic acidosis. Which
compensatory respiratory change should occur?
A. Decreased respiratory rate
B. Increased respiratory rate
C. Decreased tidal volume
,D. Increased arterial carbon dioxide
E. Decreased renal bicarbonate excretion
Answer: B. Increased respiratory rate
Rationale: Loss of bicarbonate through diarrhea causes metabolic
acidosis, which stimulates hyperventilation to reduce arterial carbon
dioxide and partially restore pH.
Question 3
A newborn has cyanosis that worsens with crying and feeding.
Echocardiography demonstrates a ventricular septal defect, overriding
aorta, pulmonary stenosis, and right ventricular hypertrophy. What
diagnosis is most likely?
A. Transposition of the great arteries
B. Tetralogy of Fallot
C. Truncus arteriosus
D. Total anomalous pulmonary venous return
E. Patent ductus arteriosus
Answer: B. Tetralogy of Fallot
Rationale: Tetralogy of Fallot consists of ventricular septal defect, right
ventricular outflow obstruction, overriding aorta, and secondary right
ventricular hypertrophy.
Question 4
,A researcher inhibits the enzyme responsible for converting pyruvate
into acetyl-CoA. Which metabolic pathway will be most directly
affected?
A. Glycolysis
B. Citric acid cycle
C. Pentose phosphate pathway
D. Glycogenolysis
E. Fatty acid synthesis
Answer: B. Citric acid cycle
Rationale: Pyruvate dehydrogenase converts pyruvate into acetyl-CoA,
which subsequently enters the citric acid cycle for oxidative
metabolism.
Question 5
A 6-month-old infant has recurrent infections with encapsulated
bacteria. Laboratory testing shows absent B cells and markedly
decreased immunoglobulin levels. Which immunodeficiency is most
likely?
A. DiGeorge syndrome
B. Chronic granulomatous disease
C. Bruton's agammaglobulinemia
D. Severe combined immunodeficiency
E. Chediak-Higashi syndrome
Answer: C. Bruton's agammaglobulinemia
, Rationale: Bruton's disease results from defective Bruton tyrosine
kinase, preventing B-cell maturation and causing profound
hypogammaglobulinemia.
Question 6
Which immunoglobulin is primarily responsible for crossing the
placenta and providing passive immunity to a fetus?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM
Answer: D. IgG
Rationale: IgG is the only major immunoglobulin class that efficiently
crosses the placenta through neonatal Fc receptor-mediated transport.
Question 7
A patient develops flushing, wheezing, hypotension, and urticaria
immediately after receiving penicillin. Which mediator is primarily
responsible for the initial vascular changes?
A. Histamine
B. Interferon-γ
C. Interleukin-2
D. Complement C3b
E. Tumor necrosis factor
COMPLETE QUESTIONS AND DETAILED SOLUTIONS
LATEST UPDATE THIS YEAR JUST RELEASED
Question 1
A 24-year-old woman has a mutation that prevents the β subunit of a
heterotrimeric G protein from exchanging GDP for GTP. Which cellular
process is most directly impaired?
A. Activation of adenylyl cyclase
B. Phosphorylation of receptor tyrosine kinases
C. Opening of voltage-gated sodium channels
D. Synthesis of phosphatidylcholine
E. Degradation of cyclic AMP
Answer: A. Activation of adenylyl cyclase
Rationale: G-protein-coupled receptors activate heterotrimeric G
proteins by promoting GDP-GTP exchange, allowing the Gα subunit to
regulate adenylyl cyclase and other effectors.
Question 2
A patient with severe diarrhea develops metabolic acidosis. Which
compensatory respiratory change should occur?
A. Decreased respiratory rate
B. Increased respiratory rate
C. Decreased tidal volume
,D. Increased arterial carbon dioxide
E. Decreased renal bicarbonate excretion
Answer: B. Increased respiratory rate
Rationale: Loss of bicarbonate through diarrhea causes metabolic
acidosis, which stimulates hyperventilation to reduce arterial carbon
dioxide and partially restore pH.
Question 3
A newborn has cyanosis that worsens with crying and feeding.
Echocardiography demonstrates a ventricular septal defect, overriding
aorta, pulmonary stenosis, and right ventricular hypertrophy. What
diagnosis is most likely?
A. Transposition of the great arteries
B. Tetralogy of Fallot
C. Truncus arteriosus
D. Total anomalous pulmonary venous return
E. Patent ductus arteriosus
Answer: B. Tetralogy of Fallot
Rationale: Tetralogy of Fallot consists of ventricular septal defect, right
ventricular outflow obstruction, overriding aorta, and secondary right
ventricular hypertrophy.
Question 4
,A researcher inhibits the enzyme responsible for converting pyruvate
into acetyl-CoA. Which metabolic pathway will be most directly
affected?
A. Glycolysis
B. Citric acid cycle
C. Pentose phosphate pathway
D. Glycogenolysis
E. Fatty acid synthesis
Answer: B. Citric acid cycle
Rationale: Pyruvate dehydrogenase converts pyruvate into acetyl-CoA,
which subsequently enters the citric acid cycle for oxidative
metabolism.
Question 5
A 6-month-old infant has recurrent infections with encapsulated
bacteria. Laboratory testing shows absent B cells and markedly
decreased immunoglobulin levels. Which immunodeficiency is most
likely?
A. DiGeorge syndrome
B. Chronic granulomatous disease
C. Bruton's agammaglobulinemia
D. Severe combined immunodeficiency
E. Chediak-Higashi syndrome
Answer: C. Bruton's agammaglobulinemia
, Rationale: Bruton's disease results from defective Bruton tyrosine
kinase, preventing B-cell maturation and causing profound
hypogammaglobulinemia.
Question 6
Which immunoglobulin is primarily responsible for crossing the
placenta and providing passive immunity to a fetus?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM
Answer: D. IgG
Rationale: IgG is the only major immunoglobulin class that efficiently
crosses the placenta through neonatal Fc receptor-mediated transport.
Question 7
A patient develops flushing, wheezing, hypotension, and urticaria
immediately after receiving penicillin. Which mediator is primarily
responsible for the initial vascular changes?
A. Histamine
B. Interferon-γ
C. Interleukin-2
D. Complement C3b
E. Tumor necrosis factor
