Selected MCQ

Current Question
In a resting mammalian cell membrane, which ion has the highest permeability and thus most strongly influences the resting membrane potential?
  • A. Sodium (Na+)
  • B. Potassium (K+)
  • C. Chloride (Cl-)
  • D. Calcium (Ca2+)
Correct Answer: B
Explanation:
At rest, cells have many open potassium leak channels, making K+ the most permeable ion. The resting membrane potential is therefore close to the K+ equilibrium potential.
Related Question 1
Overexpression of the Bcl-2 protein in a cell would most likely result in which effect?
  • A. Increased apoptosis
  • B. Enhanced autophagy
  • C. Resistance to apoptosis
  • D. Increased necrosis
Correct Answer: C
Explanation:
Bcl-2 is an anti-apoptotic protein. Its overexpression makes cells more resistant to apoptotic signals, promoting cell survival.
Related Question 2
Binding of extracellular matrix protein fibronectin to a cell’s integrin receptor most directly triggers which intracellular signaling pathway?
  • A. cAMP/PKA pathway
  • B. MAP kinase (ERK) pathway
  • C. JAK/STAT pathway
  • D. Hedgehog signaling pathway
Correct Answer: B
Explanation:
Integrin activation often activates focal adhesion kinase and the MAPK/ERK cascade, promoting cell survival and proliferation.
Related Question 3
A newly synthesized protein is destined for secretion outside the cell. Which sequence or signal will it most likely contain?
  • A. A hydrophobic transmembrane domain
  • B. A nuclear localization signal
  • C. A signal peptide at the N-terminus
  • D. A peroxisomal targeting signal at the C-terminus
Correct Answer: C
Explanation:
Secreted proteins typically have an N-terminal signal peptide that directs the ribosome to the ER for co-translational translocation into the secretory pathway.
Related Question 4
A mutation in nuclear lamin would most directly impair which cellular structure?
  • A. Alignment of chromosomes during metaphase
  • B. Anchoring of the nucleus to the cytoskeleton
  • C. Organization and structural integrity of the nuclear envelope
  • D. Export of mRNA through nuclear pores
Correct Answer: C
Explanation:
Lamins are intermediate filament proteins that form a network lining the inner nuclear membrane. Mutations disrupt the nuclear envelope’s stability and organization.
Related Question 5
A mutation prevents dynein from binding microtubules in eukaryotic cells. Which of the following processes would be most directly impaired?
  • A. Skeletal muscle contraction
  • B. Movement of vesicles from the Golgi apparatus to the endoplasmic reticulum
  • C. Movement of chromosomes toward the spindle poles during mitosis
  • D. Sliding of microtubule doublets in eukaryotic cilia and flagella
Correct Answer: D
Explanation:
Dynein motor proteins drive the sliding of microtubule doublets in cilia and flagella. Without functional dynein, ciliary and flagellar motion would be impaired. (Other processes involve myosin or different motor proteins.)