I am reading “The Immortal Life of Henrietta Lacks”. I am 57% through now. Today I am writing down the biological facts I learned so far from this book before I forget them.
1. Cervix cancer is caused by a virus called HPV-18 (Human Papilloma Virus – 18). The virus can insert its DNA into the human chromosomes. In Henrietta Lacks’ case, multiple copies of HPV-18’s DNA were found in her DNA. One of them was inserted into the long arm (q) of her chromosome 11, and mutated her p53 gene – an important tumor suppressor gene.
2. Hela cells are undergoing a different evolutionary path. Because Hela cells have been existing outside the human body for over a half century. It is certainly possible that they have taken an entirely different evolutionary path, because they are subjected to different selective pressures in a culture tube.
3. Hayflick Limit – A normal cell reaches its limit and stop dividing when it has doubled 50 times or has undertaken 50 mitotic divisions. (After Leonard Hayflick, who published a paper in 1961).
4. Cancers are inheritable if they are caused by genetic mutations, which can be passed down to the next generation. But in Henrietta’s case, her cancer was not inheritable, because it was caused by a virus, which inserted its DNA into her chromosomes and mutated a tumor-suppressor gene.
5. The reason that cancer cells can divide perpetually is that they contain an active telomerase to repair the telomeres of the chromosomes, which are shortened by each mitotic division. Whereas in normal somatic cells, telomerase is not active, so telomeres become shorter after each cell division, and to the certain point, they are too short that DNA polymerase is not able to replicate the chromosomes. So a normal cell has so-called Hayflick Limit.
