telomere
They are apart of our DNA. They protect genes. Alot of research is going into them because there is a theory of thought that says if you can extend your telomers you can live forever. they shorten every time your DNA replicates. Also from smoking lack of exercise and being having alot of fat. studies also show that short telomers are linked to heart diseases and high blood pressure.
Immortality. "A hallmark of cancer cells is immortality. The only cells in the body that are usually 'immortal' are germ cells and some stem cells. Other cells in the body are not immortal and can divide only a limited number of times before they either cease dividing or die. One block to unlimited cell division is a specialized structure at the end of each chromosome called the telomer." (Huether, McCance 2008, p 231)