Telomeretelomere

Telomeretelomere is not a standard term in biology. This article describes telomeres, the protective ends of linear chromosomes.

Telomeres are repetitive nucleotide sequences located at the ends of linear chromosomes. In humans the repeats are TTAGGG, extending several kilobases in length, and they are bound by the shelterin protein complex. Telomeres protect chromosome ends from being recognized as double-strand breaks and prevent end-to-end fusions. They also form a lariat-like T-loop that hides the terminus.

During DNA replication, the end-replication problem leads to progressive shortening of telomeres with each cell division. When critically short, cells enter replicative senescence or undergo apoptosis, linking telomere length to cellular aging. Telomere length is maintained in germ cells, some stem cells, and most cancer cells by the enzyme telomerase, which carries an RNA template (TERC) and a catalytic subunit (TERT). In many somatic tissues telomerase is silenced. A minority of cancers use the alternative lengthening of telomeres (ALT) pathway, relying on homologous recombination.

Genetic disorders of telomere biology, such as dyskeratosis congenita, arise from defects in telomerase or shelterin components and cause bone marrow failure and other problems. Telomere length can serve as a biomarker of aging and disease risk, but is influenced by genetics and environment; lifestyle factors like chronic stress and smoking have been associated with shorter telomeres in some studies, though causal links are complex.

Measurement methods include quantitative PCR for the T/S ratio, Southern blot terminal restriction fragment analysis, and newer single-telomere length assays. The study of telomeres informs aging, cancer biology, and regenerative medicine, and ongoing research seeks targeted therapies that modulate telomere maintenance.