2004, Peter M. Lansdorp, 11: Telomeres and Telomere Regulation, Robert Paul Lanza (editor), Handbook of Stem Cells, Volume 2: Adult and Fetal Stem Cells, page 127, Chromosome ends or telomeres are composed of guanine-rich repeat sequences and associated proteins. A minimum number of repeats is essential for proper telomere function and to avoid sustained activation of DNA damage pathways that may result in replicative senescence or cell death.
Source: wiktionary