Genes and Antiaging Medicine: Telomere Shortening and Antiaging

The human genome is composed of autosomes numbered 1–22 and two types of sex chromosomes (X and Y). Each chromosome is a folded double-stranded DNA molecule, a sequence of four types of bases (adenine [A], thymine [T], guanine [G], and cytosine [C]). At the ends of the chromosomes, there is a characteristic repetitive sequence called telomere DNA (in mammals, a repetition of TTAGGG). Various proteins bind to telomere DNA, and it is believed to form a loop structure. The complex of telomere DNA and proteins is called a telomere. Telomeres prevent chromosomes from accidentally fusing and contribute to the stabilization of chromosome structure. During cell division, when DNA is replicated, the normal DNA replication mechanism cannot completely replicate the very end of the chromosome. Therefore, in most cells, telomere DNA becomes shorter with each replication. Telomerase, expressed in germ cells and stem cells, can replicate the ends of chromosomes, so these cells can maintain the length of telomere DNA.