Telomeres are structures made of DNA sequences and proteins found at the ends of chromosomes. They are a widespread genetic feature most commonly found in eukaryotes. Telomeres protect the ends of chromosomes from becoming frayed or tangled, and they ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break. Telomeres are critical for maintaining genomic integrity and may be factors for age-related diseases.

Each time a cell divides, the telomeres become slightly shorter. Eventually, they become so short that the cell can no longer divide successfully, and the cell dies. This shortening process is associated with aging, cancer, and a higher risk of death. However, telomeres can be rebuilt by an enzyme called telomerase to restore cell division. Telomerase adds repeats of non-coding nitrogenous bases (5-TTAGGG-3) to the telomere structure.

In humans, telomeres play a significant role in cellular senescence with major contributions to human aging. Pathologically, dysregulated expression of the telomere synthesis mechanism causes cellular immortality, leading to potential oncogenesis and tumorigenesis. Telomeres also prevent the free ends of the chromosome from appearing as DNA double-stranded breaks, which in turn safeguards the ends from accidental DNA repair.