Telomeres are the end cap of chromosomes. They are proteins that do not participate in chromosome duplication during cell division. The number of cell divisions in all but immune and sperm cells are calculated to be 50. The cell can have a traumatic death (heat/cold/radiation/infection/blunt force) or a planned death. The planned death is called apoptosis where the cell divisions reach their limit and the cell can't make the proteins to survive. The telomere protects the end of the chromosome from binding to the end of another during duplication. It behaves like a pencil eraser in that each cell division shortens the length of the telomere until there is no longer any protection on the end. This programmed death occurs because necessary proteins cease to be made.