Practice question

Refrigerated cooling centrifuges operating at 4°C are essential during preparation of animal cells for cryopreservation and extraction of temperature-sensitive macromolecules. During harvesting for freezing, cells undergo trypsin-EDTA detachment releasing intracellular proteases, nucleases, phosphatases and apoptotic mediators. Low temperature markedly reduces metabolic rate, enzymatic degradation, and membrane lipid fluidity changes that predispose cells to lysis. Cells are pelleted at low g-force 100-300 g to avoid shear stress, washed to remove serum and residual trypsin that would interfere with DMSO cryoprotectant action, then resuspended in cold freezing medium containing fetal bovine serum and 10% DMSO. Maintaining suspension on ice between centrifugation steps prevents DMSO toxicity that is accentuated at warm temperatures and permits controlled-rate freezing at -1°C per minute using isopropanol containers. This cold handling preserves membrane integrity, intracellular ATP pools, and post-thaw plating efficiency for sensitive primary neurons, embryonic stem cells, and hybridomas compared to room temperature processing. Recovery rates improve significantly when DMSO addition is dropwise with constant agitation on ice. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.