Practice question

Necrosis involves rapid pathological loss of membrane integrity without regulated phosphatidylserine exposure or caspase activation. Propidium iodide is a membrane impermeant DNA intercalating fluorescent dye that cannot enter viable or early apoptotic cells with intact membranes. When membrane ruptures in necrosis, dye enters nucleus, binds DNA and emits bright red fluorescence detectable by cytometer. FITC alone is simply a fluorochrome tag, Annexin V marks apoptotic phosphatidylserine exposure, GFP is intrinsic fluorescent protein requiring genetic expression. PI positivity therefore distinguishes necrotic or late membrane compromised populations effectively.