Practice question

Cryopreservation enables essentially indefinite storage of mammalian cell lines and primary cells by arresting biochemical reactions at cryogenic temperatures, but prevention of lethal intracellular ice formation crucial. Dimethyl sulfoxide at 5 to 10 percent volume per volume emerged as standard cryoprotectant for most animal cells due to rapid membrane permeability coefficient 10^-5 cm per second, colligative depression of freezing point, ability to replace water molecules via hydrogen bonding and promotion of vitrification rather than crystallization that would mechanically puncture organelles and plasma membrane. During controlled slow cooling at minus 1 Celsius per minute achieved by isopropanol-filled containers Mr Frosty, DMSO reduces eutectic phase formation, limits solute concentration injury described by Mazur two-factor hypothesis balancing ice formation versus solute toxicity, stabilizes phospholipid bilayers and cytoskeleton. Compared to glycerol which permeates slower favored for insect Sf9 cells and some stem cells, DMSO offers faster equilibration but exhibits cytotoxicity at concentrations above 10 percent and temperature above 4 Celsius, necessitating quick addition at chilled state and rapid dilution with serum-containing medium post-thaw to sustain recovery above 80 percent. Ethanol and formaldehyde are toxic fixatives unsuitable for viability preservation.