Fundamental Cellular Processes

• Flow Cytometry in Cell Cycle Analysis:
• Flow cytometry is the benchmark analytical technique for determining cell cycle distribution by quantifying the cellular DNA content of thousands of individual cells in suspension:
• Cells are permeabilized and stained with a fluorescent DNA-binding dye (propidium iodide, DAPI).
• Fluorescence emission is strictly proportional to DNA content:
• $\text{G}_0/\text{G}_1$ phase cells contain diploid ($2n$) DNA.
• $\text{G}_2/\text{M}$ phase cells contain tetraploid ($4n$) DNA and display double the fluorescence intensity of $\text{G}_1$ cells.
• $\text{S}$ phase cells display an intermediate fluorescence intensity ($2n \lt \text{DNA} \lt 4n$).

Correct option: (4) Flow cytometry

• Techniques for Cell Cycle Analysis:
• Flow Cytometry: Directly quantifies DNA content distribution across $\text{G}_0/\text{G}_1$, S, and $\text{G}_2/\text{M}$ phases.
• BrdU / EdU Incorporation: Quantifies active DNA synthesis during S phase.
• Immunofluorescence: Detects single-cell phase-specific markers (e.g., phospho-histone H3 for mitosis).
• Western Blotting: Measures the bulk protein abundance of specific cell cycle regulators (e.g., cyclins or CDKs) in cell population lysates, but cannot determine the cell cycle stage or phase percentages of individual cells.

Correct option: (2) Western blotting