By the early nineties, a scientist at Yale had used HeLa to discover that human cancer cells contain an enzyme called telomerase that rebuilds their telomeres. The presence of telomerase meant cells could keep regenerating their telomeres indefinitely. This explained the mechanics of HeLa’s immortality: telomerase constantly rewound the ticking clock at the end of Henrietta’s chromosomes so they never grew old and never died. It was this immortality, and the strength with which Henrietta’s cells grew, that made it possible for HeLa to take over so many other cultures—they simply outlived and
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