Selected MCQ

Current Question
Gap junction channels between animal cells are formed by which protein?
  • A. Connexin
  • B. Cadherin
  • C. Integrin
  • D. Actin
Correct Answer: A
Explanation:
Connexins assemble into connexons that align between adjacent cells to form gap junction channels for direct cytoplasmic communication.
Related Question 1
Which organelle in animal cells contains its own circular DNA and is involved in ATP production?
  • A. Mitochondrion
  • B. Golgi apparatus
  • C. Peroxisome
  • D. Endoplasmic reticulum
Correct Answer: A
Explanation:
Mitochondria have a circular genome and produce ATP through oxidative phosphorylation.
Related Question 2
Which of the following organelles is present in plant cells but absent in animal cells?
  • A. Peroxisome
  • B. Centrosome
  • C. Chloroplast
  • D. Golgi apparatus
Correct Answer: C
Explanation:
Chloroplasts (sites of photosynthesis) are found in plant and algal cells but not in animal cells.
Related Question 3
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 4
Which chromatography technique separates proteins primarily based on size using a gel matrix?
  • A. Ion-exchange chromatography
  • B. Gel filtration (size-exclusion) chromatography
  • C. Affinity chromatography
  • D. Reverse-phase chromatography
Correct Answer: B
Explanation:
Gel filtration chromatography (size-exclusion) separates proteins by size: larger molecules elute first because they enter fewer pores in the matrix, while smaller molecules elute later.
Related Question 5
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).