COMLEX-USA Biomedical Sciences 1 — Questions and Answers
Question 1: Which enzyme is deficient in Tay-Sachs disease, leading to accumulation of GM2 ganglioside?
- Hexosaminidase A (Correct answer)
- Glucocerebrosidase
- Sphingomyelinase
- Alpha-galactosidase A
Correct answer: Hexosaminidase A
Tay-Sachs disease results from deficiency of hexosaminidase A, causing GM2 ganglioside accumulation in lysosomes.
Question 2: A mutation in which gene is most commonly associated with hereditary breast and ovarian cancer syndrome?
- TP53
- BRCA1/2 (Correct answer)
- APC
- RB1
Correct answer: BRCA1/2
BRCA1 and BRCA2 mutations are the most common inherited cause of breast and ovarian cancer syndrome.
Question 3: The 'watershed' area between the superior and inferior mesenteric artery territories, most vulnerable to ischemia, is located at:
- Hepatic flexure
- Splenic flexure (Correct answer)
- Sigmoid colon
- Cecum
Correct answer: Splenic flexure
The splenic flexure of the colon is a watershed zone between SMA and IMA territories and is most vulnerable to ischemic colitis.
Question 4: Which complement pathway is activated by antibody-antigen complexes and begins with C1q binding?
- Alternative pathway
- Lectin pathway
- Classical pathway (Correct answer)
- Terminal pathway
Correct answer: Classical pathway
The classical complement pathway is activated when C1q binds to antibody-antigen complexes, initiating the complement cascade.
Question 5: During which phase of the cell cycle does DNA replication occur?
- G1 phase
- S phase (Correct answer)
- G2 phase
- M phase
Correct answer: S phase
DNA synthesis and replication occur during S (synthesis) phase of the cell cycle.
Question 6: The sliding filament theory of muscle contraction states that sarcomere shortening results from:
- Shortening of actin and myosin filaments
- Myosin heads pulling actin toward the M line (Correct answer)
- Z-disc disintegration
- Titin protein contraction
Correct answer: Myosin heads pulling actin toward the M line
During muscle contraction, myosin heads bind actin and pull the thin filaments toward the center (M line), shortening the sarcomere without changing filament length.
COMLEX-USA Biomedical Sciences 1
Which enzyme is deficient in Tay-Sachs disease, leading to accumulation of GM2 ganglioside?