Summary

Telomerase extends telomeric DNA, overcoming the problem of incomplete replication and sequence loss at the ends of chromosomes.

In the absence of telomerase, telomeres shorten with each cell division. Excessive shortening is associated with aging and senescence of cultured human cells.

Telomere lengthening mechanisms are normally inactive in mature human cells. In cancer cells, the mechanisms become active, allowing uncontrolled cell division and growth.

Various proteins bind to telomeric DNA. These molecules protect the ends of chromosomes from degradation and inappropriate nuclear rearrangements. They also regulate the cellular machinery that maintains the telomeres.