122. Which one of the following cell separation techniques allows cells from different stages of the
cell cycle to be separated simultaneously with minimal perturbation to their physiology?
A. counterflow centrifugal elutriation
B. fluorescent activated cell sorter
C. size exclusion chromatography
D. ultracentrifugation

Detailed Explanation:

Counterflow centrifugal elutriation is a specialized cell separation technique that combines centrifugal force and fluid counterflow to sort cells based on size and density, which correlate closely with the stages of the cell cycle.

Why It Works for Cell Cycle Separation:

• Cell size increases progressively during the cell cycle. For example:

  • Cells in G1 phase are generally smaller.

  • Cells in S and G2 phases are larger due to DNA replication and growth.

• Elutriation uses a continuous flow of buffer against centrifugal force to separate these cells gently and without altering their physiological states.

This technique:

• Allows live cells to be collected without exposure to fixatives or stains.

• Minimally perturbs cellular physiology, making it ideal for studies that require downstream analysis of intact, viable cells.

Why Not the Others?

• Fluorescent Activated Cell Sorting (FACS): Requires staining and often uses DNA-binding dyes, which can alter cell physiology.

• Size exclusion chromatography: Not suited for separating live cells and offers limited resolution for similar-sized cell populations.

• Ultracentrifugation: Typically used for separating subcellular components or organelles, not live cells based on the cell cycle.

Correct Answer:

A. Counterflow centrifugal elutriation

This method uniquely enables simultaneous separation of live cells at various cell cycle stages with minimal disturbance, making it a gold standard in physiological cell cycle studies.