Schematic representation of telomere structure and telomerase complex. Telomeres are at the extremities of chromosomes. The telomeric 3′ end terminates as a single-stranded, G-rich overhang. Telomeres are capped by a protein complex (TRF1, TRF2, TPP1, POT1, TIN2, and Rap1), collectively known as shelterin, that physically shield the DNA. The telomerase complex is composed of telomerase reverse transcriptase (TERT), the RNA component (TERC), and associated proteins (dyskerin, NOP10, NHP2, GAR). TERT enzymatically adds TTAGGG nucleotide repeats to the 3′ end of telomere’s leading strand using TERC as a template. Dyskerin, NOP10, NHP2, and GAR bind to TERC and stabilize the complex.