Answer to Question 1
Some theories of aging propose that the number of times cells can divide is directly related to the length of life span of an organism. The tips of chromosomes, called telomeres, help regulate cell division. Evidence suggests that telomeres adjust a cell's response to stress and growth stimulation based upon cell divisions and DNA damage. The enzyme, telomerase, is needed in DNA replication to fully reproduce telomeres when cells divide. But telomerase is usually not present in somatic cells when they divide. The result is that with each cell division, the telomeres become shorter.
Eventually, chromosomes can't replicate because the telomeres have become too short.
Answer to Question 2
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