But they do not age. Bacteria keep on dividing forever, until some outside agency kills them. Cancer cells are similarly immortal. They keep on dividing and dividing, endlessly, unless they are killed or their host dies. Inside the nucleus of virtually every cell in your body are the long strands or filaments called chromosomes.
Human cells have forty-six chromosomes, except for the sex cells, which have half that number.
DNA makes up the cell's genes. At the tip of each spindle-shaped chromosome is a sort of cap, called a telomere. Telomeres somewhat resemble the aglets on the ends of shoelaces. The telomeres keep the ends of the chromosomes from sticking together, and from sticking onto other chromosomes. Bacterial DNA does not have telomere caps, and tends to loop itself into a ragged circle, like a snake swallowing its tail.