For one, we know that telomeres (stretches of DNA at the end of chromosomes) shorten as we age. Each time a cell divides, the telomeres get shorter. When the telomere gets too short the cell can no longer divide and dies. Normal cells reach their limit when they’ve doubled about 50 times (Hayflick’s Limit).
Cancer cells escape this fate because an enzyme called telomerase prevents the telomeres from becoming shorter.
Henrietta contracted the sexually transmitted virus called Human Papilloma Virus 18 (HPV-18), which causes cervical cancer. HPV basically inserts its DNA into the DNA of the host cell, more specifically the long arm of the eleventh chromosome. This insertion turns off the P53 tumor suppressor gene.
Scientist had not been able to grow human cells in culture before because regular cells die after 50 divisions. Therefore, Henrietta’s cells where able to grow forever because they are cancer cells. These cells no longer have program cell death and they also have very active telomerase.
