Telomerase works by adding base pairs to the overhang of DNA on the 3' end, extending the strand until DNA polymerase and an RNA primer can complete the complementary strand and successfully synthesize the double stranded DNA. Since DNA polymerase only synthesizes DNA in the leading strand direction, the shortening of the telomere results. Through their research, Blackburn and collaborators were able to show that the telomere is effectively replenished by the enzyme telomerase, which conserves cellular division by preventing the rapid loss of genetic information internal to the telomere, leading to cellular aging.