COMSAE Phase 1 Form ASA 107
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 6-year-old boy presents with recurrent respiratory infections,
chronic diarrhea, and failure to thrive. Laboratory evaluation
demonstrates defective chloride ion transport across epithelial
membranes. Which protein is most likely defective?
A. Dystrophin
B. Fibrillin-1
C. CFTR
D. Spectrin
Answer: C. CFTR
Rationale: CFTR is a chloride channel located on epithelial cells.
Mutations result in cystic fibrosis, characterized by recurrent
pulmonary infections, pancreatic insufficiency, malabsorption, and
elevated sweat chloride concentrations.
2. A researcher administers a toxin that irreversibly inhibits
cytochrome c oxidase in the mitochondrial electron transport
chain. Which complex is directly affected?
A. Complex I
B. Complex II
,C. Complex III
D. Complex IV
Answer: D. Complex IV
Rationale: Cytochrome c oxidase is Complex IV of the electron
transport chain. It transfers electrons to oxygen, the final electron
acceptor. Inhibition halts oxidative phosphorylation and ATP
generation.
3. A patient develops nephrolithiasis secondary to excessive urinary
excretion of cystine. Which transport defect is responsible?
A. Defective glucose transporter
B. Defective amino acid transporter in renal tubules
C. Defective sodium-potassium ATPase
D. Defective aquaporin channels
Answer: B. Defective amino acid transporter in renal tubules
Rationale: Cystinuria results from impaired reabsorption of cystine
and dibasic amino acids in the proximal renal tubules, causing
recurrent kidney stones.
4. During DNA replication, an enzyme synthesizes short RNA primers
necessary for DNA polymerase function. Which enzyme performs
this role?
A. Helicase
B. Primase
C. Ligase
D. Topoisomerase II
Answer: B. Primase
,Rationale: Primase synthesizes RNA primers that provide the free 3′
hydroxyl group required for DNA polymerase to initiate DNA
synthesis.
5. A newborn exhibits severe developmental abnormalities due to
defective microtubule assembly. Which cellular structure is
primarily affected?
A. Intermediate filaments
B. Actin microfilaments
C. Mitotic spindle
D. Desmosomes
Answer: C. Mitotic spindle
Rationale: Microtubules form the mitotic spindle responsible for
chromosome segregation during cell division.
6. A patient with vitamin B12 deficiency demonstrates elevated
methylmalonic acid levels. Which enzymatic reaction is impaired?
A. Homocysteine to methionine
B. Methylmalonyl-CoA to succinyl-CoA
C. Pyruvate to acetyl-CoA
D. Citrate to isocitrate
Answer: B. Methylmalonyl-CoA to succinyl-CoA
Rationale: Vitamin B12 is a cofactor for methylmalonyl-CoA mutase.
Deficiency leads to accumulation of methylmalonic acid and
neurologic manifestations.
7. A scientist studies a receptor that activates phospholipase C.
Which second messengers are generated?
A. cAMP and ATP
B. DAG and IP3
, C. GMP and cGMP
D. Calcium and ATP
Answer: B. DAG and IP3
Rationale: Phospholipase C cleaves PIP2 into diacylglycerol (DAG) and
inositol triphosphate (IP3), activating protein kinase C and increasing
intracellular calcium.
8. A patient develops megaloblastic anemia after prolonged
methotrexate therapy. Which enzyme is directly inhibited?
A. Dihydrofolate reductase
B. Thymidylate synthase
C. DNA polymerase
D. Ribonucleotide reductase
Answer: A. Dihydrofolate reductase
Rationale: Methotrexate inhibits dihydrofolate reductase, preventing
tetrahydrofolate synthesis and impairing DNA synthesis.
9. Which amino acid serves as a precursor for catecholamine
synthesis?
A. Glycine
B. Tyrosine
C. Lysine
D. Alanine
Answer: B. Tyrosine
Rationale: Tyrosine is converted to DOPA and subsequently to
dopamine, norepinephrine, and epinephrine.
10. A patient with chronic alcoholism develops Wernicke
encephalopathy. Deficiency of which cofactor is responsible?
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 6-year-old boy presents with recurrent respiratory infections,
chronic diarrhea, and failure to thrive. Laboratory evaluation
demonstrates defective chloride ion transport across epithelial
membranes. Which protein is most likely defective?
A. Dystrophin
B. Fibrillin-1
C. CFTR
D. Spectrin
Answer: C. CFTR
Rationale: CFTR is a chloride channel located on epithelial cells.
Mutations result in cystic fibrosis, characterized by recurrent
pulmonary infections, pancreatic insufficiency, malabsorption, and
elevated sweat chloride concentrations.
2. A researcher administers a toxin that irreversibly inhibits
cytochrome c oxidase in the mitochondrial electron transport
chain. Which complex is directly affected?
A. Complex I
B. Complex II
,C. Complex III
D. Complex IV
Answer: D. Complex IV
Rationale: Cytochrome c oxidase is Complex IV of the electron
transport chain. It transfers electrons to oxygen, the final electron
acceptor. Inhibition halts oxidative phosphorylation and ATP
generation.
3. A patient develops nephrolithiasis secondary to excessive urinary
excretion of cystine. Which transport defect is responsible?
A. Defective glucose transporter
B. Defective amino acid transporter in renal tubules
C. Defective sodium-potassium ATPase
D. Defective aquaporin channels
Answer: B. Defective amino acid transporter in renal tubules
Rationale: Cystinuria results from impaired reabsorption of cystine
and dibasic amino acids in the proximal renal tubules, causing
recurrent kidney stones.
4. During DNA replication, an enzyme synthesizes short RNA primers
necessary for DNA polymerase function. Which enzyme performs
this role?
A. Helicase
B. Primase
C. Ligase
D. Topoisomerase II
Answer: B. Primase
,Rationale: Primase synthesizes RNA primers that provide the free 3′
hydroxyl group required for DNA polymerase to initiate DNA
synthesis.
5. A newborn exhibits severe developmental abnormalities due to
defective microtubule assembly. Which cellular structure is
primarily affected?
A. Intermediate filaments
B. Actin microfilaments
C. Mitotic spindle
D. Desmosomes
Answer: C. Mitotic spindle
Rationale: Microtubules form the mitotic spindle responsible for
chromosome segregation during cell division.
6. A patient with vitamin B12 deficiency demonstrates elevated
methylmalonic acid levels. Which enzymatic reaction is impaired?
A. Homocysteine to methionine
B. Methylmalonyl-CoA to succinyl-CoA
C. Pyruvate to acetyl-CoA
D. Citrate to isocitrate
Answer: B. Methylmalonyl-CoA to succinyl-CoA
Rationale: Vitamin B12 is a cofactor for methylmalonyl-CoA mutase.
Deficiency leads to accumulation of methylmalonic acid and
neurologic manifestations.
7. A scientist studies a receptor that activates phospholipase C.
Which second messengers are generated?
A. cAMP and ATP
B. DAG and IP3
, C. GMP and cGMP
D. Calcium and ATP
Answer: B. DAG and IP3
Rationale: Phospholipase C cleaves PIP2 into diacylglycerol (DAG) and
inositol triphosphate (IP3), activating protein kinase C and increasing
intracellular calcium.
8. A patient develops megaloblastic anemia after prolonged
methotrexate therapy. Which enzyme is directly inhibited?
A. Dihydrofolate reductase
B. Thymidylate synthase
C. DNA polymerase
D. Ribonucleotide reductase
Answer: A. Dihydrofolate reductase
Rationale: Methotrexate inhibits dihydrofolate reductase, preventing
tetrahydrofolate synthesis and impairing DNA synthesis.
9. Which amino acid serves as a precursor for catecholamine
synthesis?
A. Glycine
B. Tyrosine
C. Lysine
D. Alanine
Answer: B. Tyrosine
Rationale: Tyrosine is converted to DOPA and subsequently to
dopamine, norepinephrine, and epinephrine.
10. A patient with chronic alcoholism develops Wernicke
encephalopathy. Deficiency of which cofactor is responsible?
