The HeLa cell line is the oldest human cell line used in molecular biology research. Every cell in a cell line has the same genes. Since their discovery, scientists have been using HeLa cells to study cancer, radiation poisoning, and infectious disease. Like most cancer cells, HeLa cells have more DNA than normal cells. HeLa cells can also divide forever without the help of scientists. In contrast, normal, non-cancerous cells can only divide a for a little while before their telomeres shorten too much and the cell cannot divide any longer. HeLa cells have a special type of active telomerase that extends telomeres during regular division.