Telomere

Telomeres are repetitive DNA sequences (TTAGGG in vertebrates) that cap the ends of linear chromosomes and protect them from degradation, end-to-end fusion, and recognition as broken DNA. Each cell division shortens telomeres slightly because DNA polymerase cannot fully replicate the very end of a linear template — the so-called end-replication problem.

When telomeres reach a critical short length, cells exit the cell cycle and enter replicative senescence, contributing to aging-related tissue decline. Telomere length is therefore a heavily studied biomarker of biological age, though it is one input among many.

Telomerase, the enzyme that lengthens telomeres, is active in stem cells and germline cells but largely silent in most somatic tissue. Several investigational longevity peptides — most prominently Epitalon — are studied for putative effects on telomerase activity.