328 OLIVE OILS AND HEALTH TELOMERES The word telomere comes from the Greek “telos” (end) and “meros” (part), and refers to the terminal regions of chromosomes containing specialised DNA sequences. mitochondria nucleus nucleolus cytoplasm; ribosome cell membrane CELL CHROMOSOME ( : telomere) DNA DNA TERMINAL telomeres These structures are found at both ends of each chromosome and help stabilise the genome by protecting it from degradation. They preserve the integrity of the cell’s DNA and play a key role in safeguarding genetic information. Telomeres also act as a record of the number of cell divisions, and their condition determines the cell’s lifespan. Once a certain number of divisions is reached, the cell enters senescence. Telomeres are composed of specific DNA sequences bound to a complex of several proteins that mark the chromosome ends. This region of DNA is non-coding (it does not synthesise proteins) and consists of a variable number of repeated nucleotide sequences. Nucleotides are the building blocks of nucleic acids (DNA and RNA). Each nucleotide consists of a sugar (ribose in RNA or deoxyribose in DNA) linked to a phosphate group and a nitrogenous base: adenine (A), cytosine (C), and guanine (G) in both DNA and RNA; thymine (T) in DNA; and uracil (U) in RNA. As part of a normal biological process, each time cells divide to multiply and regenerate body tissues, their telomeres become shorter. This shortening can be counteracted by an enzyme called telomerase, which adds DNA to the telomeres. However, telomerase activity gradually declines over time. As a result, less DNA is added, telomeres continue to shorten, and eventually become so short that the cell can no longer divide. This progressive shortening is believed to contribute to cellular ageing and is associated with the ageing of the individual. Telomerase and telomeres are of particular interest not only for understanding ageing-related changes, but also for their role in the development of cancer. Cancer cells have a remarkable ability to divide, and one of the key changes observed is that they maintain long telomeres. As a result, the molecular clock is effectively switched off, cell ageing is bypassed, and the cells can continue dividing indefinitely, becoming “immortal” and contributing to the pathological processes of cancer. The rate at which telomeres shorten can be influenced by factors that accelerate ageing, such as stress, smoking, and obesity. Shortening can also be hastened by certain diseases, including cardiovascular conditions and infections, among others; as well as by •
RkJQdWJsaXNoZXIy Njg1MjYx