Cell cycle analysis MCQs With Answer

Understanding cell cycle analysis is essential for B.Pharm students studying pharmacology, toxicology, and drug development. This concise guide focuses on cell cycle phases (G0, G1, S, G2, M), regulatory proteins (cyclins, cyclin-dependent kinases), checkpoints (G1/S, G2/M, spindle assembly), and experimental approaches such as flow cytometry, propidium iodide and BrdU/EdU staining, synchronization methods, and cell cycle inhibitors. Emphasis is placed on interpreting DNA-content histograms, identifying sub-G1 apoptotic peaks, assessing proliferation indices, and distinguishing cytostatic versus cytotoxic effects. Mastery of these topics aids design of preclinical studies and mechanistic evaluation of anticancer agents. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which phase of the cell cycle is characterized by DNA synthesis?

• G0
• G1
• S
• G2

Correct Answer: S

Q2. In flow cytometric DNA histograms using propidium iodide, which peak corresponds to cells with 2N DNA content?

• Sub-G1 peak
• G1 peak
• S-phase region
• G2/M peak

Correct Answer: G1 peak

Q3. Which reagent requires DNA denaturation and antibody detection to identify newly synthesized DNA?

• EdU (5-ethynyl-2′-deoxyuridine)
• BrdU (Bromodeoxyuridine)
• Propidium iodide
• DAPI

Correct Answer: BrdU (Bromodeoxyuridine)

Q4. Which cyclin-CDK complex primarily drives the G1 to S transition?

• Cyclin B–CDK1
• Cyclin A–CDK2
• Cyclin E–CDK2
• Cyclin D–CDK1

Correct Answer: Cyclin E–CDK2

Q5. Which synchronization method arrests cells by depolymerizing microtubules and causes mitotic arrest?

• Thymidine block
• Nocodazole treatment
• Serum starvation
• Hydroxyurea treatment

Correct Answer: Nocodazole treatment

Q6. A sub-G1 peak on a DNA-content histogram most commonly indicates:

• Cells in late G2 phase
• A population of polyploid cells
• Apoptotic cells with fragmented DNA
• Cells actively synthesizing DNA

Correct Answer: Apoptotic cells with fragmented DNA

Q7. Which technique uses click chemistry for sensitive detection of S-phase cells without DNA denaturation?

• BrdU incorporation with antibody
• EdU incorporation
• Propidium iodide staining
• Karyotyping

Correct Answer: EdU incorporation

Q8. Which protein is a marker of proliferation present in all active phases but absent in G0?

• p21
• Ki-67
• Cyclin B1
• P53

Correct Answer: Ki-67

Q9. Which checkpoint kinase is primarily activated by replication stress and single-stranded DNA?

• ATM
• ATR
• Chk2
• CDC25

Correct Answer: ATR

Q10. When preparing cells for propidium iodide DNA staining, why is RNase treatment necessary?

• To fix cells to the cytoskeleton
• To remove RNA that would otherwise contribute to fluorescence signal
• To permeabilize the plasma membrane
• To induce cell cycle arrest for synchronization

Correct Answer: To remove RNA that would otherwise contribute to fluorescence signal

Q11. Which of the following best describes the action of CDK4/6 inhibitors (e.g., palbociclib) used in cancer therapy?

• They inhibit DNA polymerase and block S phase
• They prevent microtubule polymerization and block mitosis
• They inhibit Cyclin D–CDK4/6 activity and induce G1 arrest
• They activate APC/C to trigger premature anaphase

Correct Answer: They inhibit Cyclin D–CDK4/6 activity and induce G1 arrest

Q12. In a flow cytometry histogram, an additional strong peak at near 4N DNA content suggests:

• Cell debris accumulation
• G1 arrest of the population
• Polyploidy or tetraploid population
• High proportion of apoptotic cells

Correct Answer: Polyploidy or tetraploid population

Q13. Double thymidine block is used to synchronize cells at which point?

• Mid-G1 phase
• G1/S boundary early S phase
• Metaphase of mitosis
• G2/M transition

Correct Answer: G1/S boundary early S phase

Q14. Which complex ubiquitinates securin and cyclin B to promote anaphase onset?

• SCF (Skp, Cullin, F-box) complex
• MCM helicase complex
• APC/C (anaphase promoting complex/cyclosome)
• Proteasome 20S core particle

Correct Answer: APC/C (anaphase promoting complex/cyclosome)

Q15. Calculating proliferation index (PI) from flow cytometry commonly uses which populations?

• Only sub-G1 and G1 populations
• G1, S and G2/M populations with PI = (S + G2/M)/(G1 + S + G2/M)
• Only G2/M population divided by total events
• Only S-phase fraction multiplied by 100

Correct Answer: G1, S and G2/M populations with PI = (S + G2/M)/(G1 + S + G2/M)

Q16. Which spindle assembly checkpoint component directly monitors kinetochore attachment and tension?

• Rb protein
• Mad2
• Cyclin A
• Topoisomerase II

Correct Answer: Mad2

Q17. Hydroxyurea causes cell cycle arrest by:

• Inhibiting ribonucleotide reductase and depleting dNTP pools
• Disrupting microtubules and blocking mitosis
• Intercalating into DNA and causing strand breaks
• Blocking CDK activity directly

Correct Answer: Inhibiting ribonucleotide reductase and depleting dNTP pools

Q18. Which assay is most appropriate to distinguish between cytostatic (cell cycle arrest) and cytotoxic (cell death) drug effects?

• Measurement of ATP levels only
• Combining cell cycle analysis (flow cytometry) with apoptosis markers (Annexin V, sub-G1)
• Simple cell adhesion assay
• Chromatin immunoprecipitation

Correct Answer: Combining cell cycle analysis (flow cytometry) with apoptosis markers (Annexin V, sub-G1)

Q19. FUCCI reporters visualize cell cycle dynamics in live cells by using fluorescently tagged proteins regulated by:

• DNA methylation changes during the cycle
• Ubiquitin-mediated proteolysis of cell cycle regulators
• Histone acetylation patterns specific to each phase
• Membrane potential shifts across the cycle

Correct Answer: Ubiquitin-mediated proteolysis of cell cycle regulators

Q20. Which of the following is a direct downstream effect of p53 activation after DNA damage relevant to cell cycle control?

• Activation of cyclin B–CDK1 to drive mitosis
• Transcriptional upregulation of p21 leading to CDK inhibition and G1 arrest
• Immediate triggering of APC/C to degrade cyclin A
• Inhibition of ATM kinase signaling

Correct Answer: Transcriptional upregulation of p21 leading to CDK inhibition and G1 arrest

Q21. In flow cytometry-based cell cycle analysis, why is RNase included during propidium iodide staining?

• RNase enhances PI fluorescence intensity for DNA
• RNase removes RNA that could bind PI and confound DNA measurements
• RNase is needed to permeabilize nuclear membrane
• RNase fixes cells to prevent cell loss during washes

Correct Answer: RNase removes RNA that could bind PI and confound DNA measurements

Q22. A drug that causes accumulation of cells specifically in G2 phase likely affects which target most directly?

• DNA replication fork progression
• Spindle microtubule polymerization
• Activation of CDK1/cyclin B or the G2/M checkpoint signaling
• Transcriptional initiation at G1 cyclins

Correct Answer: Activation of CDK1/cyclin B or the G2/M checkpoint signaling

Q23. Which analysis distinguishes S-phase cells by measuring incorporation of nucleotide analogues rather than total DNA content?

• Propidium iodide histogram only
• BrdU or EdU incorporation assays
• Annexin V binding assay
• Western blot for cyclin B

Correct Answer: BrdU or EdU incorporation assays

Q24. Which event directly triggers sister chromatid separation during anaphase?

• Phosphorylation of histone H3
• Ubiquitination and degradation of securin by APC/C, activating separase
• Activation of Cyclin D–CDK4/6
• Degradation of cyclin E

Correct Answer: Ubiquitination and degradation of securin by APC/C, activating separase

Q25. Serum starvation is commonly used to synchronize cells by inducing which state?

• G2 arrest
• Entry into quiescent G0 state
• Immediate apoptosis
• Permanent senescence

Correct Answer: Entry into quiescent G0 state

Q26. In drug screening, an increase in the percentage of cells in G1 with a concomitant decrease in S and G2/M suggests the compound is likely:

• Inducing mitotic catastrophe
• Inhibiting entry into S phase (G1 arrest)
• Causing DNA fragmentation and apoptosis
• Promoting tetraploidy

Correct Answer: Inhibiting entry into S phase (G1 arrest)

Q27. Which protein complex loads onto DNA replication origins to license replication in G1?

• APC/C complex
• MCM helicase complex (minichromosome maintenance proteins)
• Cyclin B–CDK1 complex
• SCF ubiquitin ligase

Correct Answer: MCM helicase complex (minichromosome maintenance proteins)

Q28. Which flow cytometric pattern indicates a successful double thymidine block synchronization released into S-phase?

• Persistent single G1 peak with no S progression
• Progression of a synchronized cohort from G1 into a broad S-phase distribution then into a clear G2/M peak
• Immediate appearance of sub-G1 apoptotic peak only
• No change in distribution compared to asynchronous culture

Correct Answer: Progression of a synchronized cohort from G1 into a broad S-phase distribution then into a clear G2/M peak

Q29. Which assay provides the most direct quantitative measure of cell cycle-dependent DNA content per cell?

• Western blot for cyclin levels
• Flow cytometry with DNA intercalating dye (e.g., PI) and RNase treatment
• Real-time PCR for cyclin transcripts
• MTT metabolic activity assay

Correct Answer: Flow cytometry with DNA intercalating dye (e.g., PI) and RNase treatment

Q30. Activation of ATM kinase in response to DNA double-strand breaks primarily leads to activation of which downstream effector that helps enforce cell cycle arrest?

• CDK4
• Chk2 and p53 signaling resulting in cell cycle arrest
• Cyclin B stabilization to promote mitosis
• Increased DNA replication origin firing

Correct Answer: Chk2 and p53 signaling resulting in cell cycle arrest

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