Selected MCQ

Current Question
Tight junctions in epithelial cells are critical because they:
  • A. Provide strong cell-cell adhesion through intermediate filaments
  • B. Allow free passage of ions between adjacent cells
  • C. Prevent leakage of solutes between cells by sealing the paracellular space
  • D. Anchor actin filaments of neighboring cells for stability
Correct Answer: C
Explanation:
Tight junctions (zonula occludens) form a seal between epithelial cells that prevents paracellular passage of ions and molecules. (Desmosomes provide intermediate filament adhesion; gap junctions allow ion passage.)
Related Question 1
In flow cytometry, cells are labeled with fluorescent antibodies and passed in a stream through a laser. This technique primarily measures:
  • A. Cell size and internal complexity
  • B. DNA sequence variants
  • C. Protein structure by X-ray diffraction
  • D. Glycolytic activity
Correct Answer: A
Explanation:
Flow cytometry measures light scattering (size and granularity) and fluorescence from labeled markers, allowing rapid analysis of cell populations (size, complexity, marker expression).
Related Question 2
Pluripotent stem cells are characterized by their ability to:
  • A. Differentiate into all cell types, including extraembryonic membranes
  • B. Differentiate into any cell type of the body (but not extraembryonic tissues)
  • C. Self-renew indefinitely but only become one cell type
  • D. Be harvested from adult muscle tissue
Correct Answer: B
Explanation:
Pluripotent stem cells (like embryonic stem cells) can form any body cell type (endoderm, mesoderm, ectoderm) but cannot form an entire organism (unlike totipotent zygotes).
Related Question 3
Which method uses an electrical pulse to introduce DNA into cells?
  • A. Microinjection
  • B. Electroporation
  • C. Lipofection
  • D. Ultracentrifugation
Correct Answer: B
Explanation:
Electroporation applies a brief high-voltage pulse to permeabilize cell membranes, transiently allowing DNA uptake.
Related Question 4
HIV is a retrovirus that carries which key enzyme for infection of host cells?
  • A. DNA-dependent DNA polymerase
  • B. Reverse transcriptase
  • C. RNA polymerase III
  • D. Integrase
Correct Answer: B
Explanation:
Retroviruses use reverse transcriptase to copy their RNA genome into DNA, which is then integrated into the host genome.
Related Question 5
Telomerase maintains chromosome ends by using a built-in RNA template. In which cells is telomerase typically active?
  • A. Most somatic cells
  • B. Germ cells and many cancer cells
  • C. Red blood cells
  • D. Neurons
Correct Answer: B
Explanation:
Telomerase is active in germline and stem cells (and reactivated in many cancers) to elongate telomeres, but is silent in most somatic cells.