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.
Telomeres keep the individual strands of DNA in our cells from looping or connecting to one another.
They also play an intriguing role in cellular aging. Some researchers believe that telomeres are a sort of cellular clock that sets the rate at which the cells age and eventually die. Each time a cell divides, its telomeres shorten. When the telomeres become short enough, cell division stops and the cell soon dies. But cancer cells regrow their telomeres after every division.