Final answer:
Telomerase is the enzyme responsible for adding telomeres to the ends of chromosomes, with a built-in RNA template that helps protect chromosome ends during replication. It is particularly active in germ cells and adult stem cells. The discovery of telomerase was awarded the Nobel Prize in 2009.
Step-by-step explanation:
The enzyme responsible for adding telomeres to the ends of chromosomes is telomerase. Telomerase is a unique enzyme that contains a catalytic part and a built-in RNA template, which functions to lengthen telomeric DNA by adding repetitive nucleotide sequences to the ends of eukaryotic chromosomes. In humans, these repetitive sequences consist of a six base-pair sequence, TTAGGG, repeated between 100 to 1000 times. The telomerase attaches to the end of the chromosome, and DNA nucleotides complementary to the RNA template are added on the 3' end of the DNA strand. Once the lagging strand template is sufficiently elongated, DNA polymerase can add the nucleotides complementary to the ends, ensuring that the chromosome’s ends are replicated and protected from degradation.
Telomerase is typically active in germ cells and adult stem cells, but not in adult somatic cells, a factor which is related to cellular aging. The discovery of telomerase and its mechanism was so significant that Elizabeth Blackburn, along with Carol W. Greider and Jack W. Szostak, was awarded the Nobel Prize for Medicine or Physiology in 2009.