STP Biomedical Sciences 2 — Questions and Answers
Question 1: Which type of cell junction prevents the passage of molecules between adjacent epithelial cells?
- Gap junction
- Tight junction (Correct answer)
- Desmosome
- Hemidesmosome
Correct answer: Tight junction
Tight junctions (zonula occludens) form a seal between epithelial cells, preventing paracellular passage of molecules.
Question 2: In Western blotting, what is the purpose of the blocking step?
- To denature the protein sample
- To prevent non-specific antibody binding (Correct answer)
- To transfer proteins to the membrane
- To separate proteins by molecular weight
Correct answer: To prevent non-specific antibody binding
Blocking with BSA or milk saturates non-specific binding sites on the membrane to reduce background signal.
Question 3: Which complement pathway is activated by mannose-binding lectin (MBL)?
- Classical pathway
- Alternative pathway
- Lectin pathway (Correct answer)
- Terminal pathway
Correct answer: Lectin pathway
MBL recognizes carbohydrate patterns on pathogens and activates complement via the lectin (MBL) pathway.
Question 4: A patient has a prolonged aPTT but normal PT. Which factor is most likely deficient?
- Factor VII
- Factor X
- Factor VIII (Correct answer)
- Factor II
Correct answer: Factor VIII
Factor VIII deficiency (hemophilia A) prolongs aPTT (intrinsic pathway) while PT (extrinsic pathway) remains normal.
Question 5: Which microscopy technique is best suited for imaging live, unstained cells without phototoxicity concerns?
- Confocal fluorescence microscopy
- Transmission electron microscopy
- Phase contrast microscopy (Correct answer)
- Scanning electron microscopy
Correct answer: Phase contrast microscopy
Phase contrast microscopy exploits differences in refractive index and requires no staining or fixation, making it ideal for live cells.
Question 6: What is the role of ubiquitin in cellular protein quality control?
- It folds misfolded proteins back to their native state
- It tags proteins for degradation by the proteasome (Correct answer)
- It prevents protein aggregation in the ER
- It transports proteins to the lysosome for secretion
Correct answer: It tags proteins for degradation by the proteasome
Polyubiquitination of misfolded or damaged proteins marks them for recognition and degradation by the 26S proteasome.
Question 7: Which cytokine is primarily responsible for inducing acute-phase protein synthesis in the liver during infection?
- IL-4
- IL-6 (Correct answer)
- IFN-γ
- IL-10
Correct answer: IL-6
IL-6 signals hepatocytes to upregulate acute-phase proteins such as C-reactive protein and fibrinogen during systemic inflammation.
STP Biomedical Sciences 2
Which type of cell junction prevents the passage of molecules between adjacent epithelial cells?