Telomerase is a polymerase enzyme found in cells that makes DNA sequences of telomeres (a special protective complex at the end of chromosomes). Telomerase is active during embryogenesis (formation and development of an embryo) until embryonic differentiation; in male germ cells (sexual reproductive cells), activated lymphocytes (a type of white blood cell) and some stem cells (unspecialized cells that can produce specific specialized cells); and in about 90% of cancer cells. In the future, the ability to regulate telomerase activity could possibly be used to slow down aging and to treat aging diseases and cancer.
Telomeres
Telomeres are a lot like aglets, the hard plastic coating on the ends of your shoelaces. Like aglets, telomeres keep your chromosomes from "fraying." Telomeres also keep your chromosomes from fusing together at the ends and from recombining. Fraying, end-to-end fusing and recombining can all cause cells to die prematurely. Human telomeres are about 10,000 nucleotides (chemicals that DNA is made of) long. Every time a cell replicates, the telomeres on the ends of the cell's chromosomes get a little shorter. Young people have long telomeres on their chromosomes; as people age, their telomeres get shorter. When the telomeres get short enough, the cell cannot replicate anymore and the cell eventually dies. This is important because the more times a cell replicates, the greater the chance for errors to be introduced into the cell DNA, which can ultimately cause disease.
Telomerase
Telomerase makes the long, repeating sequences of TTAGGG that make up a telomere at the end of a chromosome. In 1985, Greider and Blackburn identified the first telomerase enzyme in the journal Cell. There are two main parts to the enzyme, a telomere RNA piece and a telomere reverse transcriptase piece. Telomerase activity is regulated at many levels, including transcription (synthesis of messenger RNA from a DNA template), messenger RNA splicing, and maturation and modification of hTERT (a catalytic protein with reverse transcriptase activity) and hTERC (the functional RNA component of Telomerase). In the laboratory, human telomerase can be turned on by coexpressing hTERT and hTERC; however, in the body, the creation of fully functional telomerase and its subsequent activity is probably a multistep process that involves many other components and proteins.
Benefits
Without telomerase making telomeres to protect the ends of our chromosomes, we could not reproduce. It would be difficult for our bodies to fight off disease and our cells would not have a signal for when to quit replicating and might begin to replicate errors that could make us ill. Cells could mistakenly identify DNA as being damaged and activate DNA-damage response proteins (that ultimately lead to the disintegration of cells) when they are not needed.
Tumors
Both benign and malignant (cancer) tumors show telomerase activity. Telomerase is active in about 90% of the 2600 human tumor samples examined to date. Telomerase activity is thought to be linked to tumor cell immortality. As tumor cells replicate, the activity of telomerase keeps the telomeres on the chromosome from getting shorter, so the tumor cells can replicate indefinitely.
The Future
Currently, scientists are studying how telomerase functions in healthy cells and in cancer cells. Some scientists think that a more complete understanding of how telomerase works could be used to slow down the aging process, to treat premature aging diseases and to treat cancer.
Tags: aging diseases, cancer cells, cell replicates, cells replicate, cells that