Selected MCQ

Current Question
During the eukaryotic cell cycle, which checkpoint ensures that all chromosomes are correctly attached to the mitotic spindle before proceeding to anaphase?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle (metaphase) checkpoint
  • D. S-phase checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint monitors attachment of all kinetochores to spindle microtubules. It prevents the onset of anaphase until all chromosomes are properly aligned and attached.
Related Question 1
Which cell cycle checkpoint is specifically responsible for preventing the onset of anaphase until all chromosomes are properly attached to the spindle apparatus?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle assembly (metaphase) checkpoint
  • D. DNA damage checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint delays anaphase until every chromosome is correctly attached to the mitotic spindle, ensuring accurate chromosome segregation.
Related Question 2
During the G1/S transition in the eukaryotic cell cycle, phosphorylation of the retinoblastoma (Rb) protein results in which of the following?
  • A. Release of E2F transcription factors, activating S-phase gene expression
  • B. Activation of cyclin-dependent kinase inhibitors to halt cell cycle progression
  • C. Induction of apoptosis via activation of p53
  • D. Inhibition of cyclin D synthesis
Correct Answer: A
Explanation:
Phosphorylated Rb releases bound E2F transcription factors, which then activate genes required for DNA replication in S phase.
Related Question 3
Which statement correctly describes the role of nuclear pore complexes in eukaryotic cells?
  • A. They allow passive diffusion of all proteins smaller than ~100 kDa
  • B. They actively transport large molecules into and out of the nucleus
  • C. They separate the nuclear interior from the cytosol without any transport
  • D. They are the sites where rRNA is transcribed and processed
Correct Answer: B
Explanation:
Nuclear pore complexes selectively transport large molecules (such as mRNA and proteins with nuclear localization/export signals) between the nucleus and the cytoplasm. Small molecules can diffuse passively up to ~40 kDa.
Related Question 4
Why is the G0 phase considered distinct from G1 in the cell cycle?
  • A. G0 cells are rapidly dividing
  • B. G0 is a quiescent/nondividing state outside the normal cycle
  • C. G0 occurs immediately after the M phase in all cells
  • D. Cells in G0 cannot re-enter the cell cycle under any condition
Correct Answer: B
Explanation:
G0 is a resting or terminal differentiation state where cells are metabolically active but not dividing. Cells can re-enter G1 from G0 given appropriate signals.
Related Question 5
Which organelle contains hydrolytic enzymes and is involved in the degradation of cellular components during autophagy?
  • A. Lysosome
  • B. Proteasome
  • C. Golgi apparatus
  • D. Smooth endoplasmic reticulum
Correct Answer: A
Explanation:
Lysosomes contain acid hydrolases that fuse with autophagosomes to degrade cellular organelles and proteins.