Final answer:
The enzyme active in replicating DNA at the chromosomal ends in stem cells and cancer cells is telomerase, which prevents their degradation and allows for continuous cell division, playing a role in both normal cellular maintenance and oncogenesis.
Step-by-step explanation:
The enzyme that replicates DNA at the ends of chromosomes in both stem cells and cancer cells is called telomerase.
Telomerase plays a crucial role in the maintenance of chromosome integrity by extending the telomeres, which are the protective caps at the ends of linear chromosomes. Without an active telomerase, chromosomes would gradually become shorter with each cell division, eventually leading to cell death or dysfunction. This enzyme is typically active in germ cells, adult stem cells, and some cancer cells. In cancer cells, reactivation of telomerase allows these cells to multiply indefinitely, which is a characteristic of cancer's uncontrolled cell proliferation. The discovery of telomerase and its action led to Elizabeth Blackburn receiving the Nobel Prize for Medicine and Physiology in 2009. Notably, telomerase activity is largely absent in adult somatic cells, and this is associated with cellular aging.