Introduction
This quiz set on Cell cycle, apoptosis, programmed cell death and oncogenes is designed for M.Pharm students preparing for advanced topics in Microbial and Cellular Biology (MPB102T). The questions focus on regulatory checkpoints, cyclins/CDKs, tumor suppressors and oncogenes, intrinsic and extrinsic apoptotic pathways, Bcl-2 family functions, caspase cascades, and alternative programmed cell death forms such as necroptosis and autophagy. Each MCQ includes plausible distractors and concise answers to help reinforce mechanistic understanding, clinical correlations (e.g., BCR-ABL, HER2, ras) and experimental detection methods (e.g., TUNEL, Ki-67). Use these to test recall, apply concepts to drug targets, and sharpen problem-solving for exams and research.
Q1. Which phase of the cell cycle is characterized primarily by DNA synthesis?
- G0 phase
- G1 phase
- S phase
- M phase
Correct Answer: S phase
Q2. Which checkpoint prevents cells with damaged or incompletely replicated DNA from entering mitosis?
- G1/S checkpoint
- G2/M checkpoint
- Spindle assembly checkpoint
- Restriction point in late G1
Correct Answer: G2/M checkpoint
Q3. Which cyclin-CDK complex is most directly responsible for triggering entry into S phase?
- Cyclin D–CDK4/6
- Cyclin E–CDK2
- Cyclin A–CDK1
- Cyclin B–CDK1
Correct Answer: Cyclin E–CDK2
Q4. The tumor suppressor p53 primarily mediates its checkpoint function by which of the following actions?
- Directly degrading cyclins
- Activating transcription of p21 leading to CDK inhibition
- Phosphorylating Rb protein to release E2F
- Acting as an E3 ubiquitin ligase for CDKs
Correct Answer: Activating transcription of p21 leading to CDK inhibition
Q5. What is the principal role of the retinoblastoma (Rb) protein in cell-cycle control?
- Phosphorylating p53 to activate apoptosis
- Inhibiting E2F transcription factors to block S-phase entry
- Activating cyclin B to promote mitosis
- Serving as a scaffold for the apoptosome
Correct Answer: Inhibiting E2F transcription factors to block S-phase entry
Q6. Which statement best defines an oncogene?
- A gene that requires two inactivating mutations to promote cancer
- A mutated or overexpressed proto‑oncogene that gains function to promote proliferation
- A gene that always suppresses tumor formation
- A gene that encodes only structural cellular proteins
Correct Answer: A mutated or overexpressed proto‑oncogene that gains function to promote proliferation
Q7. The BCR‑ABL fusion oncogene arises most commonly through which genetic mechanism?
- Gene amplification of chromosome 17
- Point mutation in codon 12 of an oncogene
- Reciprocal chromosomal translocation t(9;22) forming the Philadelphia chromosome
- Epigenetic promoter methylation
Correct Answer: Reciprocal chromosomal translocation t(9;22) forming the Philadelphia chromosome
Q8. Activation of ras oncogenes in many cancers is typically due to which molecular change?
- Chromosomal translocation creating fusion protein
- Point mutation that impairs GTPase activity causing constitutive signaling
- Promoter hypermethylation silencing expression
- Exon deletion leading to truncated protein lacking effector domain
Correct Answer: Point mutation that impairs GTPase activity causing constitutive signaling
Q9. HER2 (ERBB2) contributes to oncogenesis mainly by which mechanism?
- Loss-of-function mutation in a nuclear transcription factor
- Gene amplification leading to overexpression of a receptor tyrosine kinase
- Secretion of a soluble growth inhibitory cytokine
- Inhibition of PI3K/AKT signaling
Correct Answer: Gene amplification leading to overexpression of a receptor tyrosine kinase
Q10. According to Knudson’s two‑hit hypothesis, which type of gene typically requires both alleles to be inactivated for tumorigenesis?
- Oncogene
- Tumor suppressor gene
- Housekeeping gene
- Proto‑oncogene
Correct Answer: Tumor suppressor gene
Q11. Which of the following morphological features is most characteristic of apoptosis?
- Cell swelling and plasma membrane rupture with inflammation
- Chromatin condensation, cell shrinkage and formation of apoptotic bodies
- Massive lysosomal rupture releasing enzymes extracellularly
- Formation of necrotic cores with neutrophil influx
Correct Answer: Chromatin condensation, cell shrinkage and formation of apoptotic bodies
Q12. Which family of proteases are the primary executors of apoptotic cell death?
- Cathepsins
- Matrix metalloproteinases (MMPs)
- Caspases
- Serine proteases of the complement system
Correct Answer: Caspases
Q13. The intrinsic (mitochondrial) apoptotic pathway is initiated by which event?
- Ligation of death receptors such as Fas/CD95
- Release of cytochrome c from mitochondria and formation of the apoptosome
- Activation of granzyme B from cytotoxic T cells only
- Extracellular matrix detachment without mitochondrial involvement
Correct Answer: Release of cytochrome c from mitochondria and formation of the apoptosome
Q14. Which Bcl‑2 family proteins function to inhibit mitochondrial outer membrane permeabilization (MOMP)?
- Bax and Bak
- Bid and Bad
- Bcl‑2 and Bcl‑xL
- Apaf‑1 and caspase‑9
Correct Answer: Bcl‑2 and Bcl‑xL
Q15. Extrinsic apoptotic signaling is primarily triggered by which molecular interaction?
- Mitochondrial release of Smac/DIABLO
- Death ligand binding to death receptors (e.g., FasL to Fas/CD95) activating caspase‑8
- Activation of caspase‑9 within the apoptosome only
- Autophagosome‑lysosome fusion leading to degradation
Correct Answer: Death ligand binding to death receptors (e.g., FasL to Fas/CD95) activating caspase‑8
Q16. Which mitochondrial protein is released during apoptosis that antagonizes inhibitor of apoptosis proteins (IAPs)?
- Cytochrome c
- Procaspase‑3
- Smac/DIABLO
- Bcl‑2
Correct Answer: Smac/DIABLO
Q17. Necroptosis is best described as which of the following?
- Apoptotic cell death mediated by caspase‑3 activation
- Programmed necrosis dependent on RIPK1/RIPK3 and MLKL that is caspase‑independent
- Autophagy‑mediated recycling of organelles for survival only
- Unregulated accidental necrosis from physical trauma
Correct Answer: Programmed necrosis dependent on RIPK1/RIPK3 and MLKL that is caspase‑independent
Q18. Autophagy primarily contributes to cell physiology by which mechanism?
- Direct activation of death receptors to induce apoptosis
- Selective degradation of intracellular components via autophagosomes for recycling and survival under stress
- Cleaving genomic DNA into nucleosomal fragments during late apoptosis
- Forming necrotic pores in the plasma membrane
Correct Answer: Selective degradation of intracellular components via autophagosomes for recycling and survival under stress
Q19. Which protein is commonly used as a proliferation marker because it is expressed in all active phases of the cell cycle but absent in resting (G0) cells?
- p21
- Ki‑67
- Caspase‑3
- Bcl‑2
Correct Answer: Ki‑67
Q20. Which laboratory assay directly detects DNA strand breaks characteristic of apoptosis in tissue sections?
- Western blot for caspase‑3
- Flow cytometry for Annexin V only
- TUNEL assay (terminal deoxynucleotidyl transferase dUTP nick end labeling)
- MTT cell proliferation assay
Correct Answer: TUNEL assay (terminal deoxynucleotidyl transferase dUTP nick end labeling)
