51.   Eventually, the telomeres become so short that the correct DNA structure is compromised and cells can no longer divide.

52.   Experiments suggest that cancer cells need IGF to escape the usual limits on the number of times a cell can divide.

53.   In normal cells, the telomeres are shortened slightly each time the cell divides.

54.   In normal cells, the DNA telomeres are shortened slightly each time a cell divides.

55.   It is believed that telomerase permits cancer cells to divide repeatedly by renewing telomeres, the end segments of chromosomes.

56.   Now we know that heart cells divide.

57.   That guards against cancer, in which cells divide wildly.

58.   The researchers watched human cells divide hundreds of times in test tubes and concluded that telomerase does not by itself turn healthy cells into malignant ones.

59.   This is done by the process of division -- an old cell divides and creates two new cells.

60.   This will permit the new cells to divide unchecked and aggregate into a tumour.