In the early 1970s, Alexey Olovnikov first recognized that chromosomes cannot completely duplicate their ends during cell division. This is known as the "end replication problem". Olovnikov proposed that every time a cell divides, a part of the DNA sequence is lost, and if this loss reaches a certain level, cell division will stop at the end. According to his "marginotomy" theory, there are sequences at the end of the DNA (telomeres) that are placed in tandem repeats and create a buffer zone that determines the number of divisions a particular cell can undergo.
Many organisms have a ribonucleoprotein enzyme called telomerase, which is responsible for adding repetitive nucleotide sequences to the ends of DNA. Telomerase replicates the telomere head and does not require ATP. In most multicellular eukaryotic organisms, telomerase is active only in germ cells, some types of stem cells such as embryonic stem cells, and certain white blood cells. Telomerase can be reactivated and telomeres restored to the embryonic state by somatic cell nuclear transfer. The continuous shortening of telomeres with each replication in somatic (body) cells may play a role in aging and in cancer prevention. This is because telomeres act as a kind of "delayed fuse" and eventually run out after a certain number of cell divisions. This action results in the loss of vital genetic information from the cell's chromosome after multiple divisions. Research on telomerase is extremely important in understanding its role in maintaining telomere length and its potential implications for aging and cancer.